University of Massachusetts Medical School Faculty Publications

Title

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

UMMS Affiliation

Department of Quantitative Health Sciences

Publication Date

9-15-2016

Document Type

Article

Disciplines

Behavior and Behavior Mechanisms | Epidemiology | Public Health

Abstract

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.

Keywords

UMCCTS funding, body mass index, endogeneity, epidemiologic methods, fixed effects, health behaviors, instrumental variables, semiparametric methods, simultaneous equations

DOI of Published Version

10.1093/aje/kww010

Source

Am J Epidemiol. 2016 Sep 15;184(6):465-76. doi: 10.1093/aje/kww010. Epub 2016 Sep 9. Link to article on publisher's site

Related Resources

Link to Article in PubMed

Journal/Book/Conference Title

American journal of epidemiology

PubMed ID

27614300

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