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The International Journal of Biostatistics

Ed. by Chambaz, Antoine / Hubbard, Alan E. / van der Laan, Mark J.

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Clarifying the Role of Principal Stratification in the Paired Availability Design

Stuart G Baker1 / Karen S Lindeman2 / Barnett S Kramer3

1National Institutes of Health

2Johns Hopkins Medical Institutions

3National Institutes of Health

Citation Information: The International Journal of Biostatistics. Volume 7, Issue 1, Pages 1–11, ISSN (Online) 1557-4679, DOI: 10.2202/1557-4679.1338, May 2011

Publication History

Published Online:
2011-05-20

The paired availability design for historical controls postulated four classes corresponding to the treatment (old or new) a participant would receive if arrival occurred during either of two time periods associated with different availabilities of treatment. These classes were later extended to other settings and called principal strata. Judea Pearl asks if principal stratification is a goal or a tool and lists four interpretations of principal stratification. In the case of the paired availability design, principal stratification is a tool that falls squarely into Pearl’s interpretation of principal stratification as “an approximation to research questions concerning population averages.” We describe the paired availability design and the important role played by principal stratification in estimating the effect of receipt of treatment in a population using data on changes in availability of treatment. We discuss the assumptions and their plausibility. We also introduce the extrapolated estimate to make the generalizability assumption more plausible. By showing why the assumptions are plausible we show why the paired availability design, which includes principal stratification as a key component, is useful for estimating the effect of receipt of treatment in a population. Thus, for our application, we answer Pearl’s challenge to clearly demonstrate the value of principal stratification.

Keywords: principal stratification; causal inference; paired availability design

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