ST06 Comparison of Correlated Proportions using SAS(R) PROC GLM: a Simulation Study.     Contributed

Dr. Mark S. Litaker Medical College of Georgia Office of Biostatistics and Bioinformatics ,Dr. Daron G. Ferris
Medical College of Georgia, Department of Family Medicine
Abstract: The performance of an analysis of variance (ANOVA) model to compare correlated proportions was evaluated using simulated data and SASŪ PROC GLM. The simulation study is based on a clinical study of three diagnostic techniques, which were evaluated for agre ement with biopsy results. 145 study subjects received two independent evaluations using each of the three methods. The data consists of 1s, representing agreement with the biopsy diagnosis, and 0s, representing disagreement. Blocks in the ANOVA represent subjects. Least-squares means and 95% confidence intervals were calculated for the three method means. Correlated observations were generated using observed subject means and hypothesized treatment effects as probabilities of agreement. Validity and power of the procedure were estimated using data simulated under the null and two alternative situations. Coverage probabilities of the confidence intervals were estimated as the proportion of replicate analyses in which the true, or simulated, probability was i ncluded in the confidence interval. Alpha for the main effect test was estimated as .058. Power to detect a difference in mean agreement among the methods was 0.66 for a difference of .10 between the extreme methods, and 0.96 for a difference of .15 betwee n the extreme methods. Funded by a grant from the NCI and AHCPR.

Biography:
Mark Litaker is an Associate Professor in the Office of Biostatistics and Bioinformatics at the Medical College of Georgia. He received a BS degree in biology from the College of Charleston, an MS degree in biostatistics from the Medical University of Sout h Carolina, and a PhD degree in biostatistics from the University of South Carolina. He has used SAS for 17 years.

Daron Ferris, MD, is the director of the Gynecologic Cancer Prevention Center and is a Professor in the Departments of Family Medicine and Obstetrics and Gynecology at the the Medical College of Georgia.