Instrumental-Variables Simultaneous Equations Model of Physical Activity and Body Mass Index: The Coronary Artery Risk Development in Young Adults (CARDIA) Study.
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.
Katie A
KA
Meyer
David K
DK
Guilkey
Hsiao-Chuen
HC
Tien
Catarina I
CI
Kiefe
Barry M
BM
Popkin
Penny
P
Gordon-Larsen
D000293:Adolescent; D000328:Adult; D000428:Alcohol Drinking / Q000009:adverse effects; D015992:Body Mass Index; D003324:Coronary Artery Disease / Q000209:etiology* / Q000517:prevention & control; D003331:Coronary Vessels / Q000473:pathology / Q000503:physiopathology*; D015444:Exercise; D057140:Fast Foods / Q000009:adverse effects; D005260:Female; D015438:Health Behavior / Q000502:physiology*; D006801:Humans; D016018:Least-Squares Analysis; D016013:Likelihood Functions; D008137:Longitudinal Studies; D008297:Male; D017533:Marital Status; D008954:Models, Biological; D015337:Multicenter Studies as Topic; D065840:Protective Factors; D017584:Reproductive History; D012111:Residence Characteristics; D018570:Risk Assessment / Q000379:methods; D012907:Smoking / Q000009:adverse effects; D055815:Young Adult
body mass index; endogeneity; epidemiologic methods; fixed effects; health behaviors; instrumental variables; semiparametric methods; simultaneous equations