Brookings: Experts - Ross A. Hammond

A Model of Food Reward Learning with Dynamic Reward Exposure

Thu, 11 Oct 2012 00:00:00 -0400

The process of conditioning via reward learning is highly relevant to the study of food choice and obesity. Learning is itself shaped by environmental exposure, with the potential for such exposures to vary substantially across individuals and across place and time. In this paper, we use computational techniques to extend a well-validated standard model of reward learning, introducing both substantial heterogeneity and dynamic reward exposures. We then apply the extended model to a food choice context.

The model produces a variety of individual behaviors and population-level patterns which are not evident from the traditional formulation, but which offer potential insights for understanding food reward learning and obesity. These include a “lock-in”effect, through which early exposure can strongly shape later reward valuation. We discuss potential implications of our results for the study and prevention of obesity, for the reward learning field, and for future experimental and computational work.

INTRODUCTION

Obesity has a complex etiology, with multiple known pathways. Considerable evidence suggests the food environment can be an important driver of obesity, and that individuals may differ in their propensity to over-consume in response to food cues in the environment. Some researchers refer to “hedonic hunger”—hunger driven by food cues and the anticipation of food pleasure rather than purely homeostatic caloric needs—underlining the importance of brain reward systems in guiding eating decisions.

We focus on the proposition that preference for high calorie foods, and the inability to resist the appeal of food cues, develops in part through a form of conditioning. Conditioning refers to the attribution of incentive properties to previously neutral cues paired with primary rewards, such as food, via learning. Individuals with an enhanced ability to learn from rewards would be more prone to this form of conditioning, and also to the related phenomenon of sensitization, which refers to a progressive increase in the neural and behavioral response to repeated rewards. Animal research strongly suggests that inherent differences in the dopamine system promote differential learning about reward-predicting cues, which in turn promotes greater motivation to consume and seek the associated reward in the presence of such cues.

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A Model of Food Reward Learning with Dynamic Reward Exposure

Authors

Ross A. Hammond
Joseph T. Ornstein
Lesley K. Fellows
Laurette Dubé
Robert Levitan
Alain Dagher

Publication: Frontiers in Computational Neuroscience

A Systems Science Perspective and Transdisciplinary Models for Food and Nutrition Security

Ross A. Hammond and Laurette Dubé — Tue, 24 Jul 2012 12:53:00 -0400

Obesity has been a major focus in the United States due to its impact on both individual health and healthcare costs. Globally, simultaneous epidemics of both obesity and malnutrition are manifestations of widespread food and nutrition insecurity, posing a pressing challenge for policymakers.

In a new paper published in the Proceedings of the National Academy of Sciences, Brookings Senior Fellow Ross Hammond and Laurette Dubé of McGill University argue that the systems that underlie food and nutrition security – including agriculture, health, and the environment – are connected to one another in ways that are often poorly understood by scientists and policymakers. The paper, “A Systems Science Perspective and Trans-disciplinary Models for Food and Nutrition Security,” proposes a “systems approach” to address the problem, leveraging new computational tools like system dynamics and agent-based modeling.

Global food security driven by multiple systems requires integrated solution. A coordinated, interdisciplinary approach is the best way to approach the problem.

Hammond and Dubé argue that these new tools, used in conjunction with the present battery of epidemiological, environmental, and macroeconomic models, will allow researchers and policymakers to better understand key dynamic and adaptive processes driving both malnutrition and obesity worldwide. “Solving food and nutrition insecurity is likely to require the interdisciplinary collaboration of many actors across society, including health professionals, agriculturalists, food industrials, policy-makers, and scientists, and the use of unconventional approaches and tools,” they write.

The authors note that interdisciplinary research is highly challenging, facing obstacles at every step in the research pipeline from education and training through the organization of research and career advancement in universities, to the process of peer review, funding, and publication. However, they conclude that policymakers can help shape the research environment to facilitate the success of such efforts, and they identify existing building blocks in the fields of agri-food, health, and environment that would allow a strategy of incremental progress from existing work toward a more comprehensive approach.

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Authors

Ross A. Hammond
Laurette Dubé

Publication: Proceedings of the National Academy of Sciences

Image Source: John Sommers II / Reuters

Next Steps in Obesity Prevention: Altering Early Life Systems To Support Healthy Parents, Infants, and Toddlers

Fri, 01 Jun 2012 00:00:00 -0400

Summary

The widespread and increasing prevalence of childhood obesity in America presents a critical public health challenge, prompting the Institute of Medicine to call for new “systems approaches” to obesity treatment and prevention. This paper, published in the focal journal Childhood Obesity, describes the role that “obesogenic systems” play in early life and proposes specific strategies for combating their effects to prevent obesity. The authors support an approach that (a) targets the earliest stages of development and (b) takes a systems perspective, simultaneously implementing changes in multiple sectors and at multiple societal levels.

To read the article, visit the publisher's website »

Authors

Philip R. Nader
Terry T.-K. Huang
Sheila Gahagan
Shiriki Kumanyika
Ross A. Hammond
Katherine Kaufer Christoffel

Publication: Childhood Obesity

Image Source: Rick Wilking / Reuters

Getting Obesity Under Control: The Importance of a Systems Approach

Ross A. Hammond — Tue, 08 May 2012 00:00:00 -0400

New research focuses on the cause and spread of the obesity epidemic and just how difficult it will be to coordinate efforts to get it under control. The epidemic not only causes serious health problems but is also driving up medical costs dramatically—by some estimates, 100 percent higher. Senior Fellow Ross Hammond examines the issues around obesity, arguing that the best way to coordinate effective prevention policies is to use a systems approach to model and coordinate the policy side, the scientific side and different methodologies. Hammond’s recent work features extensively in a major new National Academy of Sciences/Institute of Medicine (IOM) report on obesity, as well as a collaboration between the Centers for Disease Control and HBO for the event, “The Weight of the Nation.”

“The obesity epidemic has really become a very pressing problem in the United States and, actually, worldwide. Here in the U.S. two in three adults are now overweight, and one in three are obese; and among children and adolescents one in three are overweight. So these are very large numbers and there are some serious public health consequences of this. Being overweight and obese puts you at much higher risk for things like several cancers, diabetes, cardiovascular disease, and also things like asthma and arthritis.

So in addition to these public health consequences there are some real economic costs associated with [being] overweight and obese. In particular, medical spending is much higher among the overweight and obese. Some estimates say as much as one hundred percent higher. So that adds up to quite a bit in medical spending, and (again) by most estimates at least twenty-one percent of U.S. medical spending is driven by obesity already. That number could easily go up, so that is some of the economic side of it.”

Preventing obesity is the best way to stop the epidemic (1:11)

“The main thing to think about it how important prevention is with obesity, in particular, because once obesity exists there are some very powerful physiological processes and behavior patterns that are very entrenched, and it is quite difficult to reverse. This is the reason why the majority of overweight and obese children go on to be overweight and obese adults. Prevention, particularly early prevention, is really important. I think that is the fundamental focus.

Unfortunately, prevention is also hard. Obesity is a very complex syndrome that is driven by many, many different factors. In one sense it is extremely simple because it is about energy balance – energy in and energy out. If you take more energy in than you have energy out you will gain weight. It is as simple as that. On the other hand it is quite complex because the drivers of what you eat, how much physical activity you get, and what your resting metabolic rate are quite complicated and involve biology, physiology, and genetics; but [it also involves] advertising, marketing, and social norms, our agricultural system of production and distribution, the physical environment around us where we live, and how our world is structured. All of those things work together to produce different outcomes. That linkage between these different factors is less well-understood and is actually very important for trying to do policy in this space.”

A systems approach to obesity needed (2:42)

“I think there is a growing consensus that what we need to do in order to do a better job of preventing obesity is to coordinate activity across different sectors and different levels of scale, or to take what is called a “systems approach.” A systems approach means that you try to coordinate what is going on in education in schools, what is going on in transportation in urban planning, and what is going on in agriculture because all of these things are linked together, and they all drive health outcomes (for obesity in particular). They tend to be addressed from a policy perspective and from a science perspective separately. Really connecting what we are doing in a coordinated and cohesive way is extremely important for making progress on this issue.

Some of the modeling work that we do at the Center on Social Dynamics and Policy here at Brookings is helping to explore these complex linkages, both across sectors (so what is happening in the private and public sectors) but also what is happening at the different levels at the federal, state and household levels. Finally, these connections between the biology, physiology (what is happening inside of people and in their brains as they eat food and observe advertising), and what is happening around them in their physical and social environment – all of these are connected. Models can help us to understand how they work together, and how to design policies that work together to address it more holistically.”

There are three systemic barriers to preventing obesity (4:11)

“There are definitely barriers in the way; there are at least three sets. One set of barriers is institutional. On the policy side we have different departments of government for public health and for the things that actually drive public health, as well, such as education, transportation and agriculture. They are not necessarily used to working together, but they really need to to address this problem. The second set of hurdles in on the scientific side. We have different fields of science – genetics, nutrition, business – and they do not usually talk to each other or work together, either. They also need to to help us understand this problem. The third set of challenges is really methodological. We do not have tools that are good at this amount of complexity, and at helping us to manage it and design effective policies. These new tools that have arisen to address this challenge is what we really specialize in here at the [Center on Social Dynamics and Policy]. We are helping the federal government and the scientific community to apply [expertise] to the obesity epidemic.”

Two out of three overweight people live in the developing world (5:17)

“In the international context the picture looks (in some ways) very different from the United States context. In fact, a lot of obesity is occurring in the developing world. Two in three overweight people in the world are in developing countries, not in the developed world. This is a surprising statistic. In the developing world everything is changing very rapidly. Their systems of growing, producing and distributing food are changing very rapidly as they develop. Their social norms and tastes are developing very rapidly.

What you find in many developing countries is, at the same time, there is a lingering epidemic of widespread malnutrition and a new obesity epidemic which is getting quite bad. They coexist, sometimes even in the same village, or even in the same household. That is a bit of a puzzle, but I think it is because both things are driven by the same fundamental underlying systems that effect nutrition. Malnutrition and over-nutrition (which is what leads to obesity) are really part of the same problem. One of the challenges for developing countries will be to solve their malnutrition crisis without creating an obesity epidemic. That is very challenging to do and it involves coordination between the agriculture sector, and our understandings of environment and health, are how the three are all working together to produce one or the other obese effects, or sometimes both at the same time.

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Getting Obesity Under Control

Image Source: © Rick Wilking / Reuters

Obesity, Prevention, and Health Care Costs

Ross A. Hammond — Fri, 04 May 2012 00:00:00 -0400

Follow @BICampaign2012
Editor's Note: For Campaign 2012, Alice Rivlin wrote a policy brief proposing ideas for the next president on America’s health care system. The following paper is a response to Rivlin’s piece from Ross Hammond. Tom Mann also prepared a response arguing that Americans must accept the reality of today’s political polarization and challenge Washington to offer tangible solutions to the nation’s most urgent problems.

Alice Rivlin highlights the twin health care challenges facing America and the next president: covering the uninsured while curbing unsustainable increases in health care costs and their impact on the debt. She provides a compelling argument for how to address these challenges through health care legislation. I would like to focus here on the role that investment in public health and prevention can play as a complementary strategy for controlling health care spending.

Perhaps the most pressing public health challenge for the United States today is the epidemic of overweight and obesity, which is linked to an array of costly and debilitating health consequences. According to data from the National Center for Health Statistics, two in three American adults are now overweight, including one in three who are obese. A recent study also found that almost one-third of children and adolescents are overweight or obese. These rates are even higher among ethnic minorities, rural populations, and those with low income or education. The health risks associated with obesity reported by the Institute of Medicine include a much higher incidence of cardiovascular disease, diabetes, several cancers, hypertension, high cholesterol, asthma, osteoarthritis, and liver disease.

Not surprisingly, then, the obesity epidemic is a major driver of health care costs in the United States, and the costs may continue to increase significantly in the future if it is not controlled. The increased health risks for major disease that come with obesity carry not only a high social price tag but also a high economic one—relative medical costs for the obese are estimated to be 36 to 100 percent higher than for Americans of healthy weight. A 2009 study found that childhood obesity alone is responsible for $14.1 billion in direct medical costs annually. By some estimates, nearly 21 percent of all current medical spending in the United States is now obesity related. A significant proportion of these medical costs is paid by Medicaid and Medicare, and one recent analysis concluded that total Medicaid spending would be almost 12 percent lower in the absence of obesity. Beyond direct medical spending, additional costs from obesity are driven by increased rates of disability and by reduced productivity.

The impact of obesity on health care spending is likely to increase in the coming years unless further preventative steps are taken. Although recent data suggest that obesity rates may now be leveling off after a period of very rapid growth, the epidemic in children is especially worrisome because most obese children become obese adults. Childhood obesity means more chronic disease will begin earlier in life for more people—driving up lifetime costs considerably. For example, type 2 diabetes (for which obesity is a particularly strong risk factor) occurred primarily in adults until recently, but the Centers for Disease Control report that it is now beginning in childhood for more Americans. A recent report in the Journal of the American Medical Association estimates that one-third of all children born in the United States today (and one-half of all Latino and African American children) will develop type 2 diabetes in their lifetime. Even if the epidemic does not worsen, these costs are likely to prove an unsustainable burden on the health system given the long-term growth of the federal debt.

Keeping the costs of obesity from overwhelming the health care system will require a renewed focus by the next president on obesity prevention. This has the potential to contain costs much more effectively than the mere treatment of obesity-related chronic health conditions. Early childhood can be an especially important period—once obesity develops, a powerful set of physiological processes and behavior patterns make it challenging to reverse. From the perspective of health care costs, early prevention can produce substantial savings. According to an analysis in the American Journal of Public Health, as little as a 5 percent reduction in the prevalence of diabetes and hypertension would save almost $25 billion annually in medium-term health care costs.

Prevention is important, but designing effective prevention efforts remains challenging. The drivers of the obesity epidemic are complex and multifaceted, so there is likely no single solution. Continued investment in research on effective prevention strategies is needed, especially in support of what the Institute of Medicine and National Institutes of Health refer to as new “systems” approaches. Indeed, it may be critical to coordinate policy across many domains and levels of scale in order to see a rapid change in the obesity epidemic. To be most effective, prevention efforts must focus not just on educating individuals or on changing environments, but on doing both together.

The next president should take several steps to address the major public health challenge of obesity and help avoid the unsustainable health care costs it will generate:

Renew the emphasis on prevention efforts. Prevention is especially important, given the role of childhood influences in the development of overweight and the challenge of reversing obesity once entrenched.
Increase investment in public health research to develop an evidence base that supports the design and testing of powerful new prevention strategies for the future. As the scientific community emphasizes, innovative approaches are greatly needed to continue to improve how policy addresses the complex drivers of obesity.
Coordinate public policy across domains and agencies. Many policy areas “outside” of health—including education, housing, transportation, agriculture, and tax policy—have strong effects on public health and obesity. A more systemic approach that takes into account connections across these areas should be a central element in an effective obesity prevention strategy.

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Campaign 2012: The Future of Health Care

Fri, 04 May 2012 13:00:00 -0400

Event Information

May 4, 2012
1:00 PM - 2:30 PM EDT

Falk Auditorium
The Brookings Institution
1775 Massachusetts Ave., NW
Washington, DC

As America confronts the realities of an aging population and a federal budget deficit, methods for containing health care costs while improving the quality and access of care are critically important. With the Supreme Court now considering its constitutionality, the fate of the Affordable Care Act is in doubt, and Medicare costs are projected to rise rapidly. As the presidential candidates look toward the next four years, which reforms are most urgent, and is there sufficient political will to implement them? Can investments in information technology and public health make health care better and more cost-effective?

On May 4, the Campaign 2012 project at Brookings held a discussion on health care reform, the fifth in a series of forums to identify and address the 12 most critical issues facing the next president. David Nather of POLITICO Pro moderated a panel discussion with Brookings experts Alice Rivlin, Ross Hammond, Thomas Mann and Mark McClellan.

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A Systems-Based Typological Framework for Understanding the Sustainability, Scalability, and Reach of Childhood Obesity Interventions

Brandon Grimm, Ross A. Hammond and Terry T.-K. Huang — Tue, 23 Aug 2011 00:00:00 -0400

Abstract

This article proposes a systems-based framework to examine three structural dimensions of childhood obesity interventions that can impact intervention sustainability, scalability, and reach. These three dimensions are the locus of intervention drivers (top-down vs. bottom-up), the locus of change effected (policy vs. individual behavior), and the public versus private sector. Interventions focused on individual behavior change often rely on bottom-up approaches and have generally been less sustainable than policy interventions. However, top-down (government or industry) support can lead to better funding and shifts in social norms. In the public sector, top-down efforts targeting individual behavior are generally also more scalable and have wider reach to diverse communities. In the private sector, behavior-change interventions tend to have greater resources and are sustained over longer periods, even when efficacy is in question; they may also be quite scalable. In a systems approach, a combination of approaches that encompass the structural dimensions in systems space will likely be needed to significantly impact childhood obesity. Next-generation childhood obesity interventions should be able to demonstrate sustainability, scalability, and reach as benchmarks of plausible success and criteria for investment.

To read the article, visit the publisher's website »

Authors

Brandon Grimm
Ross A. Hammond
Terry T.-K. Huang

Publication: Children's Health Care Special Issue: The Treatment of Pediatric Obesity: Bringing Contexts and Systems into Focus

Social Influence and Obesity

Ross A. Hammond — Thu, 18 Nov 2010 16:38:00 -0500

ABSTRACT

Purpose of review: To review a selection of research published in the last 12 months on the role of social influence in the obesity epidemic.

Recent findings: Recent papers add evidence to previous work linking social network structures and obesity. Social norms, both eating norms and body image norms, are identified as one major source of social influence through networks. Social capital and social stress are additional types of social influence.

Summary: There is increasing evidence that social influence and social network structures are significant factors in obesity. Deeper understanding of the mechanisms of action and dynamics of social influence, and its link with other factors involved in the obesity epidemic, is an important goal for further research.

To learn more, download the full paper at Current Opinion in Endocrinology, Diabetes & Obesity »

Authors

Ross A. Hammond

Publication: Current Opinion in Endocrinology, Diabetes and Obesity

Image Source: © Rick Wilking / Reuters

The Economic Impact of Obesity in the United States

Ross A. Hammond and Ruth Levine — Tue, 14 Sep 2010 00:00:00 -0400

Abstract: Over the past several decades, obesity has grown into a major global epidemic. In the United States, more than two-thirds of adults are now overweight and one-third is obese. In this article, we provide an overview of the state of research on the likely economic impact of the US obesity epidemic at the national level. Research to date has identified at least four major categories of economic impact linked with the obesity epidemic: direct medical costs, productivity costs, transportation costs, and human capital costs. We review current evidence on each set of costs in turn, and identify important gaps for future research and potential trends in future economic impacts of obesity. Although more comprehensive analysis of costs is needed, substantial economic impacts of obesity are identified in all four categories by existing research. The magnitude of potential economic impact underscores the importance of the obesity epidemic as a focus for policy and a topic for future research.

Introduction
Over the past several decades, obesity has grown into a major global epidemic. By 2002, nearly 500 million people were overweight worldwide. In the United States (US), rates of obesity have doubled since 1970 to over 30%, with more than two-thirds of Americans now overweight. The determinants of this epidemic are likely complex, with substantial heterogeneity at the individual level in both causes and consequences that is beyond the scope of the current review.

In this article, we provide an overview of the state of research on the likely economic impact of the US obesity epidemic at the aggregate level. We conducted a broad search of the literature that addresses potential economic costs of obesity. The most recent studies that sample US populations have identified at least four major categories of economic impact linked with the obesity epidemic: direct medical costs, productivity costs, transportation costs, and human capital costs. We systematically review current evidence on each set of costs in turn, and discuss important gaps for future research along with potential trends in future economic impacts of obesity. This review adds to the current research on the economic impact of obesity by providing a more comprehensive overview of the range of effects, as well as a summary of the most up-to-date estimates.

Publication: Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy

Image Source: © Lucas Jackson / Reuters

The Economic Costs of Obesity

Ross A. Hammond — Tue, 14 Sep 2010 09:44:00 -0400

The total costs of obesity in the U.S. alone may exceed $215 billion annually, according to a new comprehensive study co-authored by Ross Hammond, senior fellow and director of the Center on Social Dynamics and Policy, and Ruth Levine. With more than two-thirds of American adults now considered overweight, and one-third obese, Hammond gives an overview of economic and policy impacts of the epidemic at the national level.

Obesity As a Public Policy Challenge
"Our study looked at the economic cost associated with the obesity epidemic which, as you know, is primarily thought of as a public health challenge here in the United States. It is associated with much higher risk of a lot of serious health conditions, including diabetes, hypertension, stroke, and so on. It also turns out that there are some economic costs associated with it. In our study, we review the evidence of what those might be. There are really several major categories. The first category is direct medical spending, and this is the category that comes about because of the higher incidence of disease associated with obesity, which means that higher health care costs are incurred by people that are obese – as much as 100% higher, in fact. Those costs add up. They might total, in the U.S., between about $86 and $147 billion a year, which is quite a bit and is very important as we think about health care cost savings and the current concern over the explosion of health care costs. Those costs have roughly doubled (perhaps) over the last decade and may continue to go up at a substantial rate until we succeed in reducing the growth in obesity rates in this country."

Health Cost Containment Threat
"We were surprised by just how large these costs really are on an annual basis here in the U.S., particularly in light of the conversation that has been going on recently about exploding health care costs and containing those health care costs. Unfortunately, obesity is something that has increased rapidly. Obesity in children is continuing to increase rapidly, and this may mean that these already substantial costs will just grow more over the next several decades and really jeopardize the health care cost containment that is being discussed now."

Obesity's Complex Causes
"Some of the things we know are drivers of obesity or associated with obesity include: certain polymorphisms of genes that are heritable; certain kinds of neuro-psychological variables that are associated with a greater risk of being obese; we know that social norms and social networks play an important role, and our media and the way people are portrayed in the media, all play a role in obesity; we know that the way our cities are built, the walkability of our cities, [and] the way our transportation infrastructure is set up plays a role in obesity; and we know that food prices and food production and the agribusiness industry play a role in the obesity epidemic. But sorting out just how much of a role each plays and how they are connected is a very complex challenge."

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Ross Hammond to Lead Center on Social Dynamics and Policy

Wed, 25 Aug 2010 13:00:00 -0400

Ross Hammond will be the new director of the Center on Social Dynamics and Policy at Brookings, Strobe Talbott announced today. Hammond is currently a senior fellow in the Economic Studies program at Brookings.

The focus of the center, formerly the Center on Social and Economic Dynamics, will continue to be on understanding the social dynamics that drive economic, political, and public health systems, but with a stronger emphasis on examining policy implications for issues such as obesity and public health preparedness.

The center’s research includes computational modeling to shed greater light on the complex determinants of chronic public health challenges, improve the planning and response to threats such as infectious disease outbreaks, and explore new policy options for combating corruption and distrust in government.

“I’m confident that with Ross’s significant experience and expertise the Center on Social Dynamics and Policy will continue to produce pioneering work at the intersection of simulation, modeling and public policy,” said Talbott. “The center’s new mission will make it even more of a resource for policymakers interested in how good data can drive good policy.”

Hammond has been at Brookings since 2006. His research focuses on modeling complex dynamics of social, economic, political, and public health systems using mathematical and agent-based computational methods. His work includes research with both the National Collaborative on Childhood Obesity Research (NCCOR) and Models of Infectious Disease Agent Study (MIDAS) networks, which have been cited by the Department of Health and Human Services for their innovation and contributions to the nation’s health.

He is also an expert member of the Network on Inequality, Complexity and Health (NICH), a new network created to apply systems science approaches to the study of health disparities. Prior to joining Brookings he was a National Science Foundation IGERT fellow at the University of Michigan’s Center for the Study of Complex Systems. He received his bachelor’s degree from Williams College and his Ph.D from the University of Michigan.

Hammond succeeds Josh Epstein, who served as director of the Center on Social and Economic Dynamics since 2007.

Systemic Risk in the Financial System: Insights from Network Science

Ross A. Hammond — Fri, 23 Oct 2009 15:52:00 -0400

Introduction

The recent financial crisis was characterized by a rapid widespread destabilization of the financial system, with little apparent warning. The crisis has led to fresh attempts to understand the structure of the financial system and what made it vulnerable to instability. One important characteristic of the system is the set of links between actors that form networks of connectivity. The structure of these networks may have enabled disruptions initially affecting only a few financial actors to rapidly spill over into a system-wide crisis.

Network structure may have played a role in the financial crisis in at least three ways:

1. Financial networks may have lacked robustness, hampering the ability of the system as a whole to continue functioning even when a few central actors stopped functioning;

2. The pattern of network links may have made the system especially susceptible to contagion (both through formal transactional links between institutions, and through informal social networks that connect both customers and individuals within institutions) ;

3. A lack of diversity in financial networks may have impaired their resilience, or ability to adapt to a new financial environment by reshaping themselves to recover functionality.

Over the past few decades, a large multidisciplinary scientific literature has developed around the mathematical study of networks—spanning fields as diverse as ecology, physics, sociology, and epidemiology. Although relatively new, this field has begun to amass a body of important findings and insights into how networks behave. In this paper, I give an overview of several key findings from network science, addressing in particular the three attributes of networks outlined above (robustness, contagion, and resilience). Where relevant, I will point out general lessons from this literature that may be of interest to regulators and reformers of the financial system—suggesting the types of structures or patterns that might be encouraged or avoided, and the kinds of data that might be useful to understand and monitor network stability.

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Publication: Pew Financial Reform Project

The Scouting Report: Flu Contagion in Schools

Wed, 21 Oct 2009 12:30:00 -0400

Event Information

October 21, 2009
12:30 PM - 1:30 PM EDT

Online Only
The Brookings Institution

Washington, DC

As the nation and the world continue to grapple with H1N1, school closures are one policy tool under consideration to slow spread of the pandemic. In the first comprehensive U.S. study of the economic cost of school and daycare center closures, Brookings’ Center on Social and Economic Dynamics (CSED) found that closing all schools in the U.S. for four weeks could cost between $10 to $47 billion dollars--a conservative estimate because only earnings rather than total compensation were used to calculate costs--and could lead to a reduction of up to 19% in key health care personnel.

On October 21, Ross Hammond, a Brookings fellow and co-author of the report, "Economic Cost and Health Care Workforce Effects of School Closures in the U.S.," and Fred Barbash, Politico senior editor, hosted a live web chat about the implications and potential costs of school closures.

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The Scouting Report Web Chat: Flu Contagion in Schools

Ross A. Hammond — Wed, 21 Oct 2009 00:00:00 -0400

As the nation and the world continued to grapple with the H1N1 virus, school closures were one policy tool under consideration to slow spread of the pandemic. In the first comprehensive U.S. study of the economic cost of school and daycare center closures, authors Howard Lempel, Ross Hammond and Joshua Epstein found that closing all schools in the U.S. for four weeks could cost between $10 to $47 billion dollars--a conservative estimate, since only earnings rather than total compensation were used to calculate costs--and could lead to a reduction of up to 19% in key health care personnel.

On October 21, Ross Hammond, a Brookings fellow and co-author of the report, "Economic Cost and Health Care Workforce Effects of School Closures in the U.S.," and Fred Barbash, Politico senior editor, hosted a live web chat about the implications and potential costs of school closures

12:29 Fred Barbash-Moderator: Good afternoon or morning, or, I suppose evening for some. Welcome to the weekly POLITICO-Brookings chat. Our guest today is Ross Hammond, a Brookings fellow and co-author of the report, "Economic Cost and Health Care Workforce Effects of School Closures in the U.S.

Thanks for being here Ross and thanks to all our readers. Let me begin Ross by asking you for a really brief summary of your study and a little bit about how you arrived at these figures.

12:30 Ross Hammond: Thanks, Fred. The purpose of our study is to give an estimate of the potential economic costs associated with widespread school closures. When schools close, parents must find a way to care for children who are at home. In some cases, this will mean adults missing work to take care of children. Those missed work hours add up to real costs to the economy (and to households).

12:31 Ross Hammond: In our study, we try to identify which households will have workers who will need to be absent to care for children, and add up the costs of those missed work hours in terms of goods and services in the economy.

12:32 Ross Hammond: We also try to estimate how many of the absentees will come from the health care sector, which could affect the delivery of health services.

12:32 [Comment From Jason] Why are school closures being discussed as a response to the flu pandemic?

12:33 Ross Hammond: Closing schools can reduce social contact among children and thus slow the spread of the virus (assuming they don’t mix elsewhere, like malls or playgrounds). Some recent studies in epidemiology have suggested that school closures could modestly reduce the total number of cases and might delay the “peak” of the epidemic, buying more time for vaccine to become available. Individual schools may also decide to close if so many of their students or staff are out ill that it is difficult to carry on their educational mission.

12:33 [Comment From Fred in VA] With H1N1 vaccine delays occurring across the country, do you think it will be more likely that we'll see a scenario like what you describe in your study?

12:34 Ross Hammond: Yes, that is certainly a possibility. The current CDC recommendation is that schools close only as a last resort, in cases of widespread illness. But if the vaccine is substantially delayed, school closure might become an important option.

12:35 [Comment From Kenneth] Where do you think swine flu will rank on the scale of pandemics?

12:35 Ross Hammond: The H1N1 epidemic is currently rated by the WHO as Phase 6 (pandemic), its highest category. It’s important to note, however, that the WHO ranking reflects how easily the virus spreads, not how sick it makes those who get it.

12:35 [Comment From Shawn] How are school closures connected with the health care workforce?

12:35 Ross Hammond: If schools close, some of the adults who will miss work to care for kids will come from the health care workforce. We estimate that this could amount to as much as 19% of the health care workforce, potentially seriously affecting the ability of the health system to treat the ill, or deliver vaccine.

12:37 [Comment From Paula] Is there any particular reason why school closures are being discussed for h1N1 this year as opposed to "normal" flu seasons?

12:38 Ross Hammond: Good question. School closures were advised in the spring because of a concern that this virus could become much more widespread, and more serious, than seasonal influenza. The H1N1 virus has continued to spread over the summer and early fall, which is unusual for flu--it's usually a very seasonal illness, beginning in late fall and early winter.

12:39 [Comment From Sally] how did you come up with those cost figures?

12:41 Ross Hammond: We used a variety of public data sources to look at households across the US, and try to evaluate where workers might have to be absent to care for children. For example, we looked to see if a household (a) had school-age children (b) had any adult who were not working full time (c) had access to any informal childcare or (d) had adults who could work from home. If a household had school-age children, all adults were working full time, none could work from home, and no informal child care was available, we assumed someone would have to miss work if schools were to close.

12:42 [Comment From Teresa] If schools are closed and children go to places like the mall or the movies, will this mitigate the usefulness of closing the school in the first place? What about the possibility of an uptick in daycare or other options where children will be in close proximity?

12:43 Ross Hammond: This is an important point. The potential benefit of school closures (and the main reason they are being considered as a public health measure) is to reduce social contact among children and slow the spread of the virus. But if kids who are not in school instead mix at the mall or playground, this reduces the potential benefit. In our study, we assume that school closures would also mean closure of day care centers and other kinds of formal child care.

12:44 [Comment From Dave] Have there been a lot of school closures thus far? I haven't heard of any in the DC area.

12:45 Ross Hammond: There were quite a few school closures last spring. This fall, there have been sporadic closures across the country, but nothing widespread as yet.

12:45 [Comment From Erin] How are the costs distributed? Who is most affected?

12:47 Ross Hammond: Unfortunately, the household costs of absenteeism due to school closure could disproportionately affect low-income households. About 20% of the projected absentees in our study would come from households with no other workers, who would have no other income if their sole wage-earner misses work. These are predominantly low income households. It’s also important to bear in mind that about 30% of American workers have no paid sick leave and may not be able to afford to miss work for childcare, and that approximately 30 million children a day rely on subsidized school meals and other services (which won’t be available if schools close).

12:48 [Comment From Eric] How can the impact of closing schools on education be measured?

12:49 Ross Hammond: In addition to the immediate costs to the economy, closing schools also results in lost learning. Estimates of this cost are around $6.1 billion per week of closure.

12:49 [Comment From Lester] Do YOU think that school closures are a good idea or a bad idea? Are they worth it?

12:52 Ross Hammond: If the epidemic becomes severe, the benefits of school closure might easily outweigh all of these costs. Several recent studies evaluate the potential benefits of school closure. The purpose of our study is to provide policymakers the best available estimates on the cost side, to enable the best possible decision-making. Whether closure is worth it or not will depend on how circumstances unfold as the pandemic continues this fall. Currently, the CDC is recommending that schools close only as a last resort.

12:53 [Comment From Diane] And, for that matter, what about large workplaces? I work in an office with a really high number of cubicles with many people working in close proximity.

12:55 Ross Hammond: Workplaces are certainly also a place where the virus can spread, and businesses are being advised to explore options for telecommuting or limiting spread at work. The current data suggests that the virus especially affects young adults and school-age children, making schools a particular policy focus.

12:56 [Comment From Diane] Has there been any discussion about swine flu and colleges/universities? It seems like college dorms would be a breeding ground for flu virus.

12:57 Ross Hammond: Colleges and universities have certainly been affected. I believe in some cases, they have even set up special temporary dorms and even classes to quarantine those with flu. Colleges and universities aren't the particular focus of our study, because closure of colleges probably wont require as many working parents to stay home.

12:58 [Comment From Ethan] Do you see swine flu getting worse this fall than it was in the spring?

12:58 Ross Hammond: Its hard to tell. We are now entering the usual season for flu, though, so it would seem reasonable to expect an uptick in cases.

12:59 [Comment From Liana] My husband had the flu last week, and when he went to the doctor, she said that they are just assuming any flu case is actually swine flu. why are doctors making this assumption? should people even bother with "normal" flu vaccines?

12:59 Ross Hammond: This is probably because "normal" flu is a very seasonal illness, and its still quite early for seasonal flu to be making an appearance. Therefore, most of the flu cases around now might be presumed to be H1N1.

1:00 [Comment From Ray] have a lot of people died from h1n1? it seems sort of crazy that smoeone could die from the flu. did people who died because of swine flu ever see a doctor?

1:01 Ross Hammond: I dont have statistics on this in front of me, but remember that about 36,000 people die from seasonal flu-related causes each year in the US, according to the CDC.

1:01 [Comment From Ben] Back to the topic of school closures. Wouldn't it make more sense to just vaccinate all school-age children than to shut schools down?

1:02 Ross Hammond: Widespread vaccination is a critical part of the current plan. It remains to be seen how quickly enough vaccine will be available.

1:06 [Comment From Paula] Is there any particular reason why school coslures are being discussed for H1n1 this year as opposed to

1:07 Ross Hammond: This is in part because the H1N1 flu seems to be spreading very quickly and widely, and also seems to affect young adults and school-age children particularly strongly.

1:10 [Comment From Karl Knapstein] There is actually discussion to close ALL the schools?!? some say the flu has run it's course (mayor blumberg) this is so much hype for a mild flu (290 deaths so far) WHY?

1:11 Ross Hammond: There was discussion about very widespread school closure in the spring; this may yet come to pass if the virus continues to spread rapidly. But in our study, we also break down the cost to a per-student, per-week cost (about $157) to allow estimates for very localized or regional closures.

1:12 [Comment From Suzanne] I've heard that CSED does modeling of things like pandemics. What exactly is modeling? Does it help predict what could happen? If so, have you done it for swine flu?

1:14 Ross Hammond: Yes, our Center on Social and Economic Dynamics here at Brookings does a lot of modeling of public health. We often use a technique called "agent-based computational modeling", in which we construct artificial socieites on computers to help understand how real ones behave, how something like a flu pandemic might unfold, and what impact various policy choices might have. We are doing some work on flu currently using these models. The school closure study doesn't use this type of modeling; its more focused on understanding the costs of the particular policy of school closure.

1:18 [Comment From Suzanne] Any sneak peak in to what you're seeing on flu so far?

1:19 Ross Hammond: Part of the difficulty in modeling the H1N1 pandemic is that it's a very new virus. We have pretty limited data to work with, and there's a lot of uncertainty about how it will behave.

1:20 [Comment From Chico] Who (or which groups) is pushing hardest for school closures? And which grade levels are they're proposing to include?

1:21 Ross Hammond: School closure is a decision made at the local level, but the CDC and other public health agencies offer guidance about criteria for when to close schools.

1:26 Fred Barbash: Thats about all the time we have for today. Ross, this has been great - thanks so much for participating.

And thanks to our readers for all your great questions. Sorry we couldn't get to them all.

1:26 Fred Barbash: Please join us next week at the same time.

Bye for now.

Authors

Ross A. Hammond

H1N1 Containment: Economic Cost and Workforce Effects of School Closures

Joshua M. Epstein, Ross A. Hammond and Howard Lempel — Wed, 30 Sep 2009 00:00:00 -0400

ABSTRACT

School closure is an important component of U.S. pandemic flu mitigation strategy. The benefit is a reduction in epidemic severity through reduction in school-age contacts. However, school closure involves two types of cost. First is the direct economic impact of the worker absenteeism generated by school closures. Second, many of the relevant absentees will be health care workers themselves, which will adversely affect the delivery of vaccine and other emergency services. Neither of these costs has been estimated in detail for the United States. We offer detailed estimates, and improve on the methodologies thus far employed in the non-U.S. literature. We give estimates of both the direct economic and health care impacts for school closure durations of 2, 4, 8, and 12 weeks under a range of assumptions. We find that closing all schools in the U.S. for four weeks could cost between $10 and $47 billion dollars (0.1-0.3% of GDP) and lead to a reduction of 6% to 19% in key health care personnel. These should be considered conservative (i.e., low) economic estimates in that earnings rather than total compensation are used to calculate costs. We also provide per student costs, so regionally heterogeneous policies can be evaluated. These estimates permit the epidemiological benefits of school closure to be compared to the costs at multiple scales and over many durations.

Introduction

School closures are an important and controversial part of the U.S. federal government’s Community Strategy for Pandemic Influenza Mitigation in the United States. Closing schools would reduce social contacts and suppress transmission. A recent literature review concludes that the direct epidemiological benefits of such a strategy are uncertain and depend on the specifics of implementation, but could include a modest (~15%) reduction in total cases and a large (~40%) reduction in peak attack rates. Controlling the peak attack rate will be crucial to prevent the U.S. healthcare system’s surge capacity from being overwhelmed. In its model scenario, the President’s Council of Advisors on Science and Technology (PCAST) finds that flu cases may demand 50 to 100 percent of the total intensive care unit (ICU) capacity in the United States. This is a major threat to a system that operates at 80 percent of capacity during normal times.

Closing schools is controversial because the epidemiological benefits come with associated costs. With their children out of school, many parents will stay home from work. This absenteeism will lead to significant economic costs. Compounding the problem, some absentees will be health care workers. The most pronounced benefit of school closure is to alleviate pressure on the health care system. But if health care absenteeism is high, the system’s capacity could be reduced when the virus is most prevalent and the demand for health care services is highest.

PCAST emphasizes the lack of research on the magnitude of these formidable costs: “Although evidence-based estimates of such costs are difficult to make and inherently imprecise, they can help to advance the rationality of the debates...” To that Center on Social and Economic Dynamics Working Paper No.55 end, this paper includes the first detailed estimate of two of these costs in the United States. We estimate the economic cost of school closure and its impact on the health care system. In addition to providing the first detailed estimate using U.S. data, we enrich the existing international literature in three ways. First, we use a more comprehensive method to identify adults who stay home to provide care. Second, when calculating the value of work missed by caretakers, our data allows us to use the caretakers’ actual wages for all caretakers who are not self-employed. Third, recent survey data enable a precise estimate of the proportion of the workforce that is able to work from home and the makeup of this segment of the workforce. We find that closing all schools in the U.S. for four weeks could cost between $10 and $47 billion dollars (0.1-0.3% of GDP) and lead to a reduction of 6% to 19% in key health care personnel.

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Complex Systems Modeling for Obesity Research

Ross A. Hammond — Mon, 15 Jun 2009 16:41:46 -0400

ABSTRACT

The obesity epidemic has grown rapidly into a major public health challenge, in the United States and worldwide. The scope and scale of the obesity epidemic motivate an urgent need for well-crafted policy interventions to prevent further spread and (potentially) to reverse the epidemic. Yet several attributes of the epidemic make it an especially challenging problem both to study and to combat. This article shows that these attributes — the great breadth in levels of scale involved, the substantial diversity of relevant actors, and the multiplicity of mechanisms implicated — are characteristic of a complex adaptive system. It argues that the obesity epidemic is driven by such a system and that lessons and techniques from the field of complexity science can help inform both scientific study of obesity and effective policies to combat obesity. The article gives an overview of modeling techniques especially well suited to study the rich and complex dynamics of obesity and to inform policy design.

Read the full paper at CDC.gov »
View U.S. Obesity Trends 1985–2007 »

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Ross A. Hammond

Publication: Preventing Chronic Disease

Containing the Spread of Swine Flu and Other Diseases through Dynamic Modeling

Tue, 28 Apr 2009 12:00:00 -0400

When cases of swine flu rose in the United States and around the world in 2009, health officials took action to contain the spread and severity of the disease. Ross Hammond discussed the artificial society models he helped develop that can aid professionals in better understanding how to prepare for and react to epidemics.

Transcript

"This has the potential to be scary. It’s a frightening downside if this gets more serious. At the moment, the indications are that it’s fairly limited to the United States. I think I would encourage everyone to pay close attention, to keep abreast of the latest news, and to follow any instructions they may receive from the public health authorities who really are on top of this. A lot of our research shows that even the best public policies that we have available can be undermined if people are unaware of what they are supposed to be doing or don’t follow the directions they are given. So, I think that’s quite important, but at the moment no one is being asked to do anything in most of the United States except to be vigilant, and I think that makes sense."

"...This particular epidemic caught everyone in the public health community by surprise, a little bit, because we were prepared for an avian flu – a so called H5M1 flu – and this is actually a fairly different virus, and we are still learning more about it and how it behaves and we have to retool our models for that. But, at CSED what we do is we build artificial society models where we are able to, on computers, reconstruct some of the dynamics of an epidemic and understand a little bit better what kinds of interventions might be effective and how people should best respond."

"...There have been some careful estimates done for an avian pandemic flu of what the macroeconomic costs could be. If it were a really severe flu, like the one we had in 1918, the Congressional Budget Office estimates that it could affect GDP by as much as four percent. At the moment that doesn’t seem usually likely because as I say it’s been fairly limited in the U.S., but if it were take a turn for the worst that’s certainly a possibility. Those economic costs come partly in the form of decreased demand as everyone stays home, doesn’t go shopping, doesn’t go out to eat, and also partly in the form of productivity losses — people who call in sick or need to stay home to care for a loved one. So that’s a real possibility, but we hope it doesn’t come to that."

"...A lot has changed since 1918, for better and for worse actually. We certainly have a lot more information at our fingertips, we have done a lot more study and preparation. It’s also the case that the transportation networks are very — it’s a much more connected world than it was in 1918, and that’s actually a disadvantage because it means that something like a flu can spread very rapidly around the world, so we have to be vigilant to prevent against that occurring. I would say that what we have learned from studying 1918 is that timing is really important in all sorts of public health interventions – both when you put something like a quarantine or travel restrictions or school closings in place and when you lift it. And there is some evidence in 1918 that they didn’t apply these measures fast enough or they lifted them too early and this can lead to multiple waves of infection, so we would like to avoid that. I think there is very close attention being paid to deploy these interventions the moment they become necessary."

Coupled Contagion Dynamics of Fear and Disease: Mathematical and Computational Explorations

Derek Cummings, Joshua M. Epstein, Ross A. Hammond and Jon Parker — Mon, 15 Dec 2008 13:46:20 -0500

Published version of the CSED October 2007 Working Paper

ABSTRACT

Background

In classical mathematical epidemiology, individuals do not adapt their contact behavior during epidemics. They do not endogenously engage, for example, in social distancing based on fear. Yet, adaptive behavior is well-documented in true epidemics. We explore the effect of including such behavior in models of epidemic dynamics.

Methodology/Principal Findings

Using both nonlinear dynamical systems and agent-based computation, we model two interacting contagion processes: one of disease and one of fear of the disease. Individuals can “contract” fear through contact with individuals who are infected with the disease (the sick), infected with fear only (the scared), and infected with both fear and disease (the sick and scared). Scared individuals–whether sick or not–may remove themselves from circulation with some probability, which affects the contact dynamic, and thus the disease epidemic proper. If we allow individuals to recover from fear and return to circulation, the coupled dynamics become quite rich, and can include multiple waves of infection. We also study flight as a behavioral response.

Conclusions/Significance

In a spatially extended setting, even relatively small levels of fear-inspired flight can have a dramatic impact on spatio-temporal epidemic dynamics. Self-isolation and spatial flight are only two of many possible actions that fear-infected individuals may take. Our main point is that behavioral adaptation of some sort must be considered.”

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Publication: PLoS One Journal

A Complex Systems Approach to Understanding and Combating the Obesity Epidemic

Ross A. Hammond — Tue, 17 Jun 2008 12:00:00 -0400

This CSED Working Paper will be included in the forthcoming "Obesity Prevention" book.

Abstract

The obesity epidemic represents a major and rapidly growing public health challenge, in the United States, and worldwide. The scope and scale of the obesity epidemic highlight the urgent need for well-crafted policy interventions to prevent further spread and (potentially) to reverse the tide. Yet several characteristics make obesity an especially challenging problem both to study, and to combat. I show that these challenges—the great breadth in levels of scale involved, the substantial diversity of relevant actors, and the multiplicity of mechanisms implicated—are characteristic of complex adaptive systems. I argue that the obesity epidemic represents such a system, and that both general lessons and techniques from the field of complexity science can help inform effective policy to combat obesity. In particular, I argue that the technique of agent-based computational modeling is especially well suited to the study of the rich and complex dynamics of obesity.

Background

The obesity epidemic represents a major and rapidly growing public health challenge, in the United States, and worldwide. Between 1970 and 2000, for example, the percentage of Americans classified as obese doubled to almost 30% (Bray, Bouchard and James 2003), with fully two-thirds of American now classified as overweight (Ogden 2006). The problem of obesity is not limited to the American context—similar epidemics of obesity are underway across the globe, from Europe to South America to the Middle East and Asia (see, for example, Rennie & Jebb 2005; Cameron et al. 2003; Yumuk 2005; Mohammedpour-Ahranjania et al. 2004; Kain et al. 2002; and Albala et al. 2002). Overall, nearly half a billion worldwide were overweight or obese in 2002 (Rossner 2002).

These sharp increases in obesity rates have significant implications for public health, since obesity is linked with diabetes, high blood pressure, and high cholesterol (NHLBI 1998). In addition to higher mortality/morbidity, obesity increases health care costs dramatically (Finkelstein et al. 2005)—some estimates suggest that obesity-related medical expenses accounted for as much as 9% of total U.S. medical expenditures in 1998 (or roughly $78.5 billion), a proportion that is expected to increase (Finkelstein, Fiebelkorn, and Wang 2003).

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Ross A. Hammond

A Complex Systems Approach to Understanding and Reversing the Obesity Epidemic

Ross A. Hammond — Thu, 08 Nov 2007 12:00:00 -0500

CSED Fellow Ross A. Hammond recently gave a major address at the 2007 McGill Health Challenge Think Tank. This event brought together top international obesity experts—from academia, government, industry, and non-profit—to work toward a comprehensive, multi-level, multi-sector approach to the worldwide obesity pandemic.

Hammond was invited to discuss how Complex Systems insights and techniques, as pioneered at CSED, can play a key role in facilitating this integrated approach. The event drew key international scientists, stakeholders, and decision-makers, including representatives from the Food and Health Organization of the United Nations, the World Health Organization, the CDC, the Culinary Institute of America, the Clinton Foundation/American Heart Association’s Alliance for a Healthier Generation and the Robert Wood Johnson Foundation, as well as from Unilever, PepsiCo, Kellogg, Sodexho, and from major US and European research universities.

Go to conference web site »

Authors

Ross A. Hammond

Publication: 2007 Health Challenge Think Tank