1. A method of pretesting items for subsequent presentation to participants in a group, the method comprising the steps of: storing, in a database, records defining a class of potential participants, each record specifying a participant and values for a plurality of predictor variables; analyzing the database to identify a cohort of records associated with participants who (i) are not in the group and (ii) have predictor-variable values similar to predictor-variable values associated with participants in the group; and pretesting the items with at least some of the participants in the cohort.