Suppose that you want to uncover the effect of having a third child on the likelihood of whether the mother will work fo

[answerhappygod]

Suppose that you want to uncover the effect of having a third
child on the likelihood of whether the mother will work for pay or
not. Since whether women with two children give birth to a third
child depends on many things, the instrumental variable that is
whether the first two children are of the same gender is used.
Please briefly discuss why the variable of whether the first two
children are of the same gender can be used as the instrumental
variable.