1. The dataset contains the variable samesex, which equals 1 if the mom's first two children are of the same sex and 0 otherwise. Is samesex a good predictor of whether a mom is likely to have a third child?
2. Explain why samesex is likely to be a valid instrument for morekids in Model 1. In your explanation, address the two conditions necessary for an instrument to be considered valid.

How does fertility affect the labor supply? In other words, how do women's contributions to the labor force change in response to having an additional child? In this problem set, you will estimate the effect of fertility on labor supply using census data. The dataset is fertility.csy. The dataset includes 254,654 observations. Each observation is a mother between the ages of 21 and 35. Table 1: Variable Descriptions Variable Description morekids =1 if mom had more than 2 children boy1sti if 1st child was a boy boy2nd =1 if 2nd child was a boy samesex =1 if 1st two children same sex agem1 age of mom at census black =1 if mom is black hispan =1 if mom is Hispanic othrace =1 if mom is not black, Hispanic or white weeksm1 |mom's weeks worked last year