Abstract: Matched sampling is a method for selecting units from a large reservoir of potential controls to produce a control group of modest size that is similar to a treated group with respect to the distribution of observed covariates. We illustrate the use of multivariate matching methods in an observational study of the effects of prenatal exposure to barbiturates on subsequent psychological development. A key idea is the use of the propensity score as a distinct matching variable.

INTRODUCTION: BACKGROUND; WHY MATCH?

Matched Sampling in Observational Studies. In many observational studies, there is a relatively small group of subjects exposed to a treatment and a much larger group of control subjects not exposed. When the costs associated with obtaining outcome or response data from subjects are high, some sampling of the control reservoir is often necessary. Matched sampling attempts to choose the controls for further study so that they are similar to the treated subjects with respect to background variables measured on all subjects.

The Danish Cohort. We examine multivariate matched sampling using initial data from a proposed study of the effects on psychological development of prenatal exposure to barbiturates. The analyses presented are preliminary and intended only to explore methodological options; none of the matched samples are the actual ones to be used for study of in utero exposure to barbiturates. The children under study were born between 1959 and 1961 and have been the object of other studies (e.g., Mednick et al. 1971; Zachau-Christiansen and Ross 1975).