Earnings Profile : Ability and Schooling: Comment

John Hause's paper is addressed to the perplexing matters of how to disentangle the effects of ability and schooling on worker earnings, and of the effect of ability on earnings over a worker's lifetime.' His emphasis oil "ability" and schooling as determinants of earnings is surely not intended to deny that other variables also affect earnings or to deny that these other variables may also interact with ability and schooling level-but he barely touches on other variables or the possibility of interactions