In a market where quality requirements are extremely high; the ultimate goal is to improve test quality and reduce the occurrence of test escapes. A customer return is a test escape which passes all tests but fails in the field. This paper analyzes seven lots of parametric wafer probe test data, where each lot contains one customer return. We ask a fundamental question: What subset of tests provides the best screening of customer returns? This leads us to the problem of selecting sets of important tests which contain necessary information to identify each customer return. We compare and combine three test selection methods and suggest an outlier analysis based test strategy for screening potential customer returns.