This work was supported in part by grants from the Centers for Disease Control and Prevention (CDC), the National Institute of Child Health and Human Development (NICHD), and the Laura Jane Musser Foundation (LJMF). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the CDC, the NICHD, or the LJMF.
This work benefited greatly from 10 anonymous peer reviews. We gratefully thank these individuals for their wonderful suggestions and comments. In addition, we thank Jennifer Rappaport, the editorial board at Oxford University Press, and countless colleagues and students who contributed in one way or another to this work.