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Soc Sci Med. 2017 Nov;192:112-124. doi: 10.1016/j.socscimed.2017.09.020. Epub 2017 Sep 21.

Re-evaluating associations between the Supplemental Nutrition Assistance Program participation and body mass index in the context of unmeasured confounders.

Author information

1
Quantitative Sciences Unit, Stanford University School of Medicine, 1070 Arastradero Rd #3C3104 MC 5559, Palo Alto, CA 94304, United States. Electronic address: jrigdon@stanford.edu.
2
General Internal Medicine and Diabetes, Massachusetts General Hospital, 50 Staniford St., 9th Floor, Boston, MA 02114, United States. Electronic address: SABerkowitz@mgh.harvard.edu.
3
Division of General Internal Medicine, University of California San Francisco, 1001 Potrero Ave, San Francisco, CA 94110, United States. Electronic address: Hilary.Seligman@ucsf.edu.
4
Stanford University School of Medicine, 1070 Arastradero Rd, Palo Alto, CA 94304, United States. Electronic address: basus@stanford.edu.

Abstract

OBJECTIVE:

To evaluate the association between participation in the Supplemental Nutrition Assistance Program (SNAP) and body mass index (BMI) in the presence of unmeasured confounding.

METHODS:

We applied new matching methods to determine whether previous reports of associations between SNAP participation and BMI were robust to unmeasured confounders. We applied near-far matching, which strengthens standard matching by combining it with instrumental variables analysis, to the nationally-representative National Household Food Acquisition and Purchasing Survey (FoodAPS, N = 10,360, years 2012-13).

RESULTS:

In ordinary least squares regressions controlling for individual demographic and socioeconomic characteristics, SNAP was associated with increased BMI (+1.23 kg/m2, 95% CI: 0.84, 1.63). While propensity-score-based analysis replicated this finding, using instrumental variables analysis and particularly near-far matching to strengthen the instruments' discriminatory power revealed the association between SNAP and BMI was likely confounded by unmeasured covariates (+0.21 kg/m2, 95% CI: -3.88, 4.29).

CONCLUSIONS:

Previous reports of an association between SNAP and obesity should be viewed with caution, and use of near-far matching may assist similar assessments of health effects of social programs.

KEYWORDS:

Instrumental variables; Near-far matching; SNAP; Social epidemiology; Weak instruments

PMID:
28965002
PMCID:
PMC5815398
DOI:
10.1016/j.socscimed.2017.09.020
[Indexed for MEDLINE]
Free PMC Article

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