As market researchers, we strive to create conjoint models that are predictive of actual purchase behavior. But it is difficult to both design good validation studies and convince the owners of the data to let one publicly share the results. This paper by James J. Tumbusch of MarketVision Research, Inc. (originally published in the 1991 Sawtooth Software Conference Proceedings) presents a compelling real-world validation of conjoint and ACA. Conjoint predictions are compared with traditional concept testing for four different frequently purchased product categories. High correlations were found--even though the conjoint and concept test samples were independent, and the conjoint studies preceded the concept test data collection by up to 12 months.