Supervised by

direction of Professor Sally W. Thurston and received the Master of Arts degree from the University of Rochester in 2005. ii Acknowledgements Many thanks to Sally Thurston for advising the completion of this dissertation. I would also like to thank my other committee members for their time and effort. I wish to thank Shanna Swan for providing data from the Study for Future families, which inspired my research. I am very appreciative of David Oakes for including me on his environmental statistics training grant from the National Institute of Environmental Health Sciences and I am grateful to Phil Davidson and Gary Myers for the opportunity to work on the Seychelles Child Development Study. I am very thankful to all the staff in the department for their help, especially Cheryl Bliss-Clark. Last but not least, I want to thank Chris and my family for their encouragement and support throughout my graduate studies. This dissertation is dedicated to my mother, whose journey inspired me to pursue biostatistics