where Rt is the excess return to some asset in month t, RMRFt is the month t value-weighted market return minus the risk-free rate, and the terms SMBt (small minus big), HMLt (high minus low), and Momentumt, are the month t returns on zero-investment factor-mimicking portfolios designed to capture size, book to-market, and momentum effects, respectively. Although there is ongoing debate about whether these factors are proxies for risk, we take no position on this issue and simply view the four-factor model as a method of performance attribution. Thus, we interpret the estimated intercept coefficient, "alpha," as the abnormal re turn in excess of what could have been achieved by passive investments in the factor