DOI: 10.5061/dryad.7f140
title: Data from: The statistical mechanics of human weight change

description: Over the past 35 years there has been a near doubling in the worldwide
 prevalence of obesity. Body Mass Index (BMI) distributions in high-income
 societies have increasingly shifted rightwards, corresponding to increases
 in average BMI that are due to well-studied changes in the socioeconomic
 environment. However, in addition to this shift, BMI distributions have
 also shown marked changes in their particular shape over time, exhibiting
 an ongoing right-skewed broadening that is not well understood. Here, we
 compile and analyze the largest data set so far of year-over-year BMI
 changes. The data confirm that, on average, heavy individuals become
 lighter while light individuals become heavier year-over-year, and also
 show that year-over-year BMI evolution is characterized by fluctuations
 with a magnitude that is linearly proportional to BMI. We find that the
 distribution of human BMIs is intrinsically dynamic—due to the short-term
 variability of human weight—and its shape is determined by a balance
 between deterministic drift towards a natural set point and diffusion
 resulting from random fluctuations in, e.g., diet and physical activity.
 We formulate a stochastic mathematical model for BMI dynamics, deriving a
 theoretical shape for the BMI distribution and offering a mechanism that
 may explain the right-skewed broadening of BMI distributions over time. An
 extension of the base model investigates the hypothesis that peer-to-peer
 social influence plays a role in BMI dynamics. While including this effect
 improves the fit with the data, indicating that correlations in the
 behavior of individuals with similar BMI may be important for BMI
 dynamics, testing social transmission against other plausible unmodeled
 effects and interpretations remains the subject of future work.
 Implications of our findings on the dynamics of BMI distributions for
 public health interventions are discussed.
description: Northwestern Medicine
 BMI dataNorthwestern Medicine
 (NU) data are stored in NU.csv comma separated values (CSV) format. This
 file contains five columns: year t, BMI in year t, BMI in year t + 1, age
 in year t, and gender. Note: When BMI in year t + 1 is unavailable then
 the entry in the third column is -1.NU.csvBRFSS BMI dataBRFSS data are stored in BRFSS BMI.csv in CSV format. This file contains two columns: year t, BMI in year t.BRFSS_BMI.csvSelf Reported NHANES BMI dataSelf-reported NHANES data are stored in NHANES SR.csv in CSV format. This file contains five colums: year t, BMI in year t − 1 (i.e. year prior to the interview), BMI in year t (i.e. at time of interview), age in year t, and gender. Note 1: We associate NHANES data from survey 1999-2000 with t = 1999, from survey 2001-2002 with t = 2001, and so on. Note 2: Because self-reported NHANES data are only used for individual-level computations, NHANES SR.csv only records data from respondents who reported both (a) BMI at time of NHANES interview and (b) BMI one year prior to NHANES interview.NHANES_SR.csvNHANES Directly Measured BMI dataDirectly measured NHANES data are stored in NHANES DM.csv in CSV format. This file contains four columns: year t, BMI in year t, age in year t, and gender. Note: We associate NHANES data from survey 1999-2000 with t = 1999, from survey 2001-2002 with t = 2001, and so on.NHANES_DM.csv