Correspondence concerning this article should be addressed to Megan M. McClelland, Human Development and Family Sciences, 245 Hallie E. Ford Center for Healthy Children and Families, Oregon State University, Corvallis, OR 97331; Phone: (541) 737-9225; Fax: (541) 737-2072. E-mail may be sent to megan.mcclelland@oregonstate.edu.
Acknowledgements: We are very grateful to Robin Corley for assistance with data management.