Studts, Christina Ruth 1971-, "Improving screening for externalizing behavior problems in very young children : applications of item response theory to evaluate instruments in pediatric primary care." (2008) My family has also been a constant source of encouragement and strength. My parents, Bob and Kathy Clark, instilled in me a love of learning, a passion to achieve, and a focus on concern for others. My sister and fellow lifelong student, Jeannie ClarkMabey, has shared in the joys of returning to school in our 30s. My husband Jamie and daughter Shannon have endured my constant attachment to the computer and endless monologues about data analyses, all the while offering unconditional love and support..v Special thanks to Jamie for inspiring me as a dedicated and accomplished scientistpractitioner, and to Shannon for being such a good napper. My family has been with me every step of the way-and for Shannon, I mean that literally.My gratitude also goes to Ruth Huber and Norma Melton-bosslady and Queen of the doctoral program, respectively-who have kept me moving forward, reminded me of deadlines, and generously provided assistance and nurturing along the way. Ruth and Norma provide a remarkable foundation for the Kent School doctoral students with their unwavering support.Dana Sullivan and Janet Carpenter were my "unofficial" committee members, offering encouragement, advice, and cheerleading from qualifying exams through the defense. I thank them for their humor, wisdom, and listening skills, and for counseling sessions and camaraderie over good meals, by phone, and even in the gyms of strange cities.Thanks also to Barbara Donadio and the physicians, staff, and patients of Duke Externalizing behavior problems in very young children are associated with an array of negative and costly long-term outcomes. Pediatric primary care is a promising venue for implementing screening practices to improve early identification of this social and public health problem. In this setting, screening requires a brief, easily scored instrument which can detect sub-clinical to clinical levels of the latent construct within the context of early childhood development. Further, items used should perform consistently with children of all sociodemographic backgrounds. This study applied item response theory analyses to investigate the precision, utility, and differential item functioning (DIF) of items measuring externalizing behavior problems in two caregiverreport questionnaires: the PSC-17 and the BPI (Peterson & Zill, 1986;Zill, 1990). Caregivers (N = 900) of children ages 3 to 5 responded to both instruments and a sociodemographic questionnaire in the waiting rooms of four pediatric primary care clinics. Sociodemographic characteristics of the children were diverse: 47% were female, 50% were of minority race, and 43% were of low socioeconomic status viii (SES). Eighteen items comprising the instruments' combined externalizing subscales were evaluated for (a) levels of externalizing behavior problems best measured, and (b) DIF exhib...