Instrumental-Variables Simultaneous Equations Model of Physical Activity and Body Mass Index: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

Meyer, Katie A.; Guilkey, David K.; Tien, Hsiao-Chuan; Kiefe, Catarina I.; Popkin, Barry M.; & Gordon-Larsen, Penny. (2016). Instrumental-Variables Simultaneous Equations Model of Physical Activity and Body Mass Index: The Coronary Artery Risk Development in Young Adults (CARDIA) Study. American Journal of Epidemiology, 184(6), 465-76. PMCID: PMC5023789

Meyer, Katie A.; Guilkey, David K.; Tien, Hsiao-Chuan; Kiefe, Catarina I.; Popkin, Barry M.; & Gordon-Larsen, Penny. (2016). Instrumental-Variables Simultaneous Equations Model of Physical Activity and Body Mass Index: The Coronary Artery Risk Development in Young Adults (CARDIA) Study. American Journal of Epidemiology, 184(6), 465-76. PMCID: PMC5023789

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We used full-system-estimation instrumental-variables simultaneous equations modeling (IV-SEM) to examine physical activity relative to body mass index (BMI; weight (kg)/height (m)(2)) using 25 years of data (1985/1986 to 2010/2011) from the Coronary Artery Risk Development in Young Adults (CARDIA) Study (n = 5,115; ages 18-30 years at enrollment). Neighborhood environment and sociodemographic instruments were used to characterize physical activity, fast-food consumption, smoking, alcohol consumption, marriage, and childbearing (women) and to predict BMI using semiparametric full-information maximum likelihood estimation to control for unobserved time-invariant and time-varying residual confounding and differential measurement error through model-derived discrete random effects. Comparing robust-variance ordinary least squares, random-effects regression, fixed-effects regression, single-equation-estimation IV-SEM, and full-system-estimation IV-SEM, estimates from random- and fixed-effects models and the full-system-estimation IV-SEM were unexpectedly similar, despite the lack of control for residual confounding with the random-effects estimator. Ordinary least squares tended to overstate the significance of health behaviors in BMI, while results from single-equation-estimation IV-SEM were notably different, revealing the impact of weak instruments in standard instrumental-variable methods. Our robust findings for fixed effects (which does not require instruments but has a high cost in lost degrees of freedom) and full-system-estimation IV-SEM (vs. standard IV-SEM) demonstrate potential for a full-system-estimation IV-SEM method even with weak instruments.




JOUR



Meyer, Katie A.
Guilkey, David K.
Tien, Hsiao-Chuan
Kiefe, Catarina I.
Popkin, Barry M.
Gordon-Larsen, Penny



2016


American Journal of Epidemiology

184

6

465-76








PMC5023789


9437

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