PROSPECTIVE INDIVIDUAL MATCHING - COVARIATE BALANCE AND POWER IN A COMPARATIVE-STUDY

In phase II to phase IV studies, randomization has gained widespread a cceptance as a methodologic tool for the allocation of patients to tre atment. However, randomization is not always feasible. At times, the t reatment intervention occurs universally throughout one or more units (for example, a hospital unit), while the control therapy is the only intervention provided in other units. Patients may arrive randomly at a unit, based solely on availability of the unit to accept new subject s. Thus, the treatment assignment process is out of the investigator's control and not subject to selection bias. We describe a prospective individual matching procedure through which one can achieve balanced a llocation of subjects to treatment groups in this comparative study se tting. In this paper, we compare balance of baseline covariates and po wer for this design, in which the subject is selected at random and as signed to a treatment group, and the traditional randomized block desi gn, in which the treatment is chosen at random and assigned to a subje ct. We show that the prospective individual matching procedure compare s favourably to the traditional randomized blocked design with respect to both baseline covariate comparability and statistical power. (C) 1 998 John Wiley & Sons, Ltd.