US population model

To evaluate the potential effects of interventions on obesity rates and health outcomes, the Childhood Obesity Intervention Cost-Effectiveness Study (CHOICES) created a computer-simulation model of the US population in 2010. This simulated US population is used as a “natural history” to which the CHOICES project can compare potential effects of specific obesity prevention interventions on future obesity rates and health outcomes.

The model produces a “virtual” population of individuals by matching data on current demographic- and state-specific data on BMI, food intake, and physical activity from the US Census, National Health and Nutrition Examination Survey, and other sources. The model then follows these individuals over time as they gain or lose weight, get sick, and incur health expenditures.

BMI trajectories

Being overweight during childhood and adolescence increase risk of being overweight as an adult. However, some overweight children become normal-weight adults and many normal-weight children become overweight adults. This is called “natural uncertainty.”

The CHOICES model simulates millions of individual BMI trajectories matched to the US population in 2010. These trajectories are constructed by combining longitudinal observations of BMI in children and adults from large datasets, including the National Longitudinal Survey of Youth, Population Study of Income Dynamics, and National Health and Nutrition Evaluation Surveys.1

Using these real BMI trajectories, the CHOICES model incorporates natural uncertainty about BMI change across the lifecourse following completion of obesity prevention interventions conducted during childhood.

Physical activity trajectories

Almost half of children ages 6-11 achieve the recommended 60 minutes of physical activity per day. However, as children transition into adolescence, physical activity levels decline precipitously, with fewer than 1 in 10 adolescents meeting physical activity guidelines.2 Physical activity levels continue to decline into adulthood.3 Only 3.5% of adults aged 20-59 achieved the recommended 30 minutes per day of moderate to vigorous physical activity on 5 out of 7 days per week.4

Although physical activity typically declines as a population ages, individuals who are active earlier in their lives tend to be active at later developmental stages. The CHOICES model incorporates the average natural history of physical activity over the lifecourse, as well as how physical activity levels track within individuals. Based on this observed tracking of physical activity over time, interventions that increase physical activity during childhood would be expected to have a small but lasting effect on lifelong physical activity trajectories and related risk of disease and death.

References

1. Goldhaber-Fiebert JD, Rubinfeld RE, Bhattacharya J, Robinson TN, Wise PH. The utility of childhood and adolescent obesity assessment in relation to adult health. Med Decis Making. 2013 Feb;33(2):163-75. doi: 10.1177/0272989X12447240. Epub 2012 May 29. PubMed PMID: 22647830.
Abstract: http://mdm.sagepub.com/content/33/2/163.abstract

2. Jones RA, Hinkley T, Okely AD, Salmon J. Tracking physical activity and sedentary behavior in childhood: a systematic review. Am J Prev Med. Jun 2013;44(6):651-658.
Abstract: http://www.sciencedirect.com/science/article/pii/S074937971300175X

3. Telama R. Tracking of physical activity from childhood to adulthood: a review. Obesity facts. 2009;2(3):187-195.
Abstract: http://www.ncbi.nlm.nih.gov/pubmed/20054224

4. Troiano RP, Berrigan D, Dodd KW, Masse LC, Tilert T, McDowell M. Physical activity in the United States measured by accelerometer. Medicine and science in sports and exercise. Jan 2008;40(1):181-188.
Abstract: http://www.ncbi.nlm.nih.gov/pubmed/18091006