Twin Data that Made a Big Difference, and that Deserve to be Better-Known and Used in Teaching

ABSTRACT

Because of their efficiency and ability to keep many other factors constant, twin studies have a special appeal for investigators. Just as with any teaching dataset, a “matched-sets” dataset used to illustrate a statistical model should be compelling, still relevant, and valid. Indeed, such a “model dataset” should meet the same tests for worthiness that news organization editors impose on their journalists: are the data new? Are they true? Do they matter? This article introduces and shares a twin dataset that meets, to a large extent, these criteria. In fact, while more than two decades old, the data are still widely cited today in ongoing related research. This dataset was the basis of a clever study that confirmed an inspired hunch, changed the way pregnancies in HIV-positive mothers are managed, and led to reductions in the rates of maternal-to-child transmission of HIV.

KEYWORDS:

• Epidemiology
• Generalized estimating equations
• Global health
• HIV
• Matched pairs
• Natural experiment
• Odds ratios
• Quasi-likelihood
• Recall bias

Acknowledgments

We thank Dr. James Goedert, Dr. Anne-Marie Duliège, Myhanh Dotrang, and the skeptical student in JH's course BIOS601 in 2011.

Supplemental Material

Supplementary materials include the Appendix with R Code to reproduce Table 1, Table 2, and the analysis results. Supplemental data for this article can be accessed on the publisher's website.