Explaining changes in married mothers' employment over time.

Employment of married mothers with preschool children rose dramatically between 1971 and 1990. Using CPS data, we find that about one-fifth of the increase in labor supply can be attributed to changes in mothers' demographic characteristics (age, education, and number of children). Changes in the earnings opportunities of new mothers and their husbands explain another one-fifth of the growth in employment. Over the two decades, infants up to three months old became less of a barrier to employment, while women's labor supply became more sensitive to their own earnings opportunities and less sensitive to those of their husbands.