1.Empirical evidence from Mincer wage equation produce rate of return estimates of roughly 10 percent, but it is commonly argued that "ability bias" may distort these estimates.Should ability bias cause rate of return estimates to be overstated or understated relative to "true" (unbiased) returns? Discuss the main potential sources of bias that can arise in the estimation of the coefficient on the years of schooling (S). Explain how the use of twin studies can help remove some of these biases.