This article analyzes the relationship between hours of work and labor force participation (LFP) in Heckman's model, Cogan's fixed-cost model, Moffitt's minimum hours constraint model, and a generalized version of Heckman's model. First, the parameter restrictions between the LFP and reduced-form hours-of-work equations are compared. The models are then estimated, and the results support the weakening of the link between the LFP and hours-of-work decisions. One implication of the analysis is that Heckman's model overstates the standard labor supply elasticities because it confounds the direct effect on labor supply with the participation effect.

This article uses very detailed information on graduates of the University of Michigan Law School to examine male-female pay differences in that population. Men and women in this population have virtually identical human capital on graduation from law school, allowing us to examine carefully the different impact of children and work history on men's and women's careers and earnings. Taking time from work in order to care for children reduces wages significantly, but a rich set of controls, including childcare, work history, school performance, and job setting measures, still leave one-fourth to one-third of the earnings gap unexplained.