Statistics Papers
Document Type
Technical Report
Date of this Version
10-2016
Publication Source
Journal of the American Statistical Association
Volume
111
Issue
515
Start Page
1157
Last Page
1167
DOI
10.1080/01621459.2015.1076342
Abstract
The informal folklore of observational studies claims that if an irrelevant observed covariate is left uncontrolled, say unmatched, then it will influence treatment assignment in haphazard ways, thereby diminishing the biases from unmeasured covariates. We prove a result along these lines: it is true, in a certain sense, to a limited degree, under certain conditions. Alas, the conditions are neither inconsequential nor easy to check in empirical work; indeed, they are often dubious, more often implausible. We suggest the result is most useful in the computerized construction of a second control group, where the investigator can see more in available data without necessarily believing the required conditions. One of the two control groups controls for the possibly irrelevant observed covariate, the other control group either leaves it uncontrolled or forces separation; therefore, the investigator views one situation from two angles under different assumptions. A pair of sensitivity analyses for the two control groups is coordinated by a weighted Holm or recycling procedure built around the possibility of slight attenuation of bias in one control group. Issues are illustrated using an observational study of the possible effects of cigarette smoking as a cause of increased homocysteine levels, a risk factor for cardiovascular disease. Supplementary materials for this article are available online.
Copyright/Permission Statement
This is an Accepted Manuscript of an article accepted by Taylor & Francis for publication in the Journal of the American Statistical Association and posted online 7 August 2015, available online: http://amstat.tandfonline.com/10.1080/01621459.2015.1076342.
Keywords
attenuation of unmeasured biases, casual inference, observational study, second control group, sensitivity analysis
Recommended Citation
Pimentel, S. D., Small, D. S., & Rosenbaum, P. R. (2016). Constructed Second Control Groups and Attenuation of Unmeasured Biases. Journal of the American Statistical Association, 111 (515), 1157-1167. http://dx.doi.org/10.1080/01621459.2015.1076342
Included in
Business Analytics Commons, Management Sciences and Quantitative Methods Commons, Statistics and Probability Commons
Date Posted: 25 October 2018
This document has been peer reviewed.