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Title: Obesity status transitions across the elementary years: Use of Markov chain modeling

Author
item CHEN, TZU - Children'S Nutrition Research Center (CNRC)
item BARANOWSKI, TOM - Children'S Nutrition Research Center (CNRC)
item MORENO, JENNETTE - Children'S Nutrition Research Center (CNRC)
item O'CONNOR, TERESIA - Children'S Nutrition Research Center (CNRC)
item HUGHES, SHERYL - Children'S Nutrition Research Center (CNRC)
item BARANOWSKI, JANICE - Children'S Nutrition Research Center (CNRC)
item WOEHLER, DEBORAH - The Cluthe And William B Oliver Foundation
item KIMBRO, RACHEL - Rice University
item JOHNSTON, CRAIG - Children'S Nutrition Research Center (CNRC)

Submitted to: Pediatric Obesity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2015
Publication Date: 4/1/2016
Citation: Chen, T.A., Baranowski, T., Moreno, J.P., O'Connor, T.M., Hughes, S.O., Baranowski, J., Woehler, D., Kimbro, R.T., Johnston, C.A. 2016. Obesity status transitions across the elementary years: Use of Markov chain modeling. Pediatric Obesity. 11(2):88-94.

Interpretive Summary: Our previous analysis of differences in means of Body Mass Index (BMI) at 11 times across 5 years among 7,000+ elementary school children indicated that the children tended to put on weight during the summer vacation and lose weight during the school year. Two limitations of these analyses are it's not clear 1) if the seasonal changes occurred with everyone in the group experiencing the small changes reflected in the mean, or large subgroups had opposing big swings in BMI; and 2) what the contribution to obesity status was with those small changes in average BMI. In the current analyses transitions into overweight or obese categories were generally small, but increased during the summer vacation, and transitions out increased during the school year, with larger transitions among boys, Hispanic and non-Hispanic Black, and lower socio-economic status children. Although the transitions were small from time to time, they accumulated across the 5+ years indicating a relentless increase in overweight and obesity in elementary school. Obesity prevention programs should begin early in elementary school and target summer vacation behaviors.

Technical Abstract: Overweight and obesity status transition probabilities using first-order Markov transition models applied to elementary school children were assessed. Complete longitudinal data across eleven assessments were available from 1,494 elementary school children (from 7,599 students in 41 out of 45 schools in a Southeast Texas school district) from kindergarten to the beginning of 5th grade. Heights and weights were measured by trained school nurses using standard procedures at the beginning and end of each school year for the 11 consecutive assessments. To estimate the transition probabilities, first order three-state (healthy weight, overweight, and obese) Markov transition models were fit to the longitudinal weight status data of all assessment periods. While there was a gradual shift to more children in the overweight or obese category over five years, children were most likely to stay in the same weight category as the previous assessment. A consistent seasonal difference in the probability of changing weight status category was seen, with a greater probability of becoming overweight and obese during the summer compared to the school year. The transition probabilities to obesity were higher among boys, Hispanic and non-Hispanic Black, and lower socio-economic status children. This study provides the first application of a Markov transition model to child weight status data. The transitions into the overweight and obese categories were small, but persistent, with smaller percentages transitioning out of overweight or obese. Early monitoring and summer intervention strategies are needed to prevent the slow, but relentless, transition into the overweight and obese categories.