Market productivity is often greater, and leisure and other household activities more enjoyable, when people perform them simultaneously. Beyond pointing out the positive externalities of synchronicity, economists have not attempted to identify exogenous causes that affect timing. We develop a...

Testosterone, which induces sexual differentiation of the male fetus, is believed to transfer from males to their littermates in placental mammals. Among humans, individuals with a male twin have been found to exhibit greater masculinization of sexually dimorphic attributes relative to those...

Recent research postulating that the diffusion of confidential access to the birth control pill to young women in the United States contributed to the dramatic social changes of the late 1960s and 1970s has not adequately accounted for the largely contemporaneous diffusion of access to abortion....