A statistical method for designing screening studies involving several experimental treatments compared to a standard treatment is developed. The screening study identifies the most promising experimental treatments which then undergo more rigorous evaluation in a future larger study. The technique is especially relevant for biopharmaceutical research and development in which phase II clinical trials are conducted to identify the most promising drug regimens which then move on to phase III of clinical development. It is assumed that the underlying distribution of the primary efficacy random variable is a qualitative/quantitative mixture. The proposed methodology involves calculating the probability of