The question regarding the determinants of the earning differential between two population groups at a given time period, and of its evolvement over time has been given continuous attention over the past three decades. The difference of the market prices of various endowments has also been called "discrimination" and measures were suggested for its quantification. In this study we present alternative formulations for the evaluation of the endowments vs. the market factors. We recommend the one which is the most consistent and symmetric over groups and show its performance for U.S. data.