JSM 2005 Online Program

Abstract #304706

This is the preliminary program for the 2005 Joint Statistical Meetings in Minneapolis, Minnesota. Currently included in this program is the "technical" program, schedule of invited, topic contributed, regular contributed and poster sessions; Continuing Education courses (August 7-10, 2005); and Committee and Business Meetings. This on-line program will be updated frequently to reflect the most current revisions.

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Activity Number:	187
Type:	Contributed
Date/Time:	Monday, August 8, 2005 : 2:00 PM to 3:50 PM
Sponsor:	Biometrics Section
Abstract - #304706
Title:	Stratification on Baseline Measure: The Variance Effect
Author(s):	Misook Park*+ and Robert E. Johnson
Companies:	Virginia Commonwealth University and Virginia Commonwealth University
Address:	Box 980032, Richmond, VA, 23298-0032, United States
Keywords:	cluster randomization ; nested effect ; intra-cluster correlaton ; pre-post correlation
Abstract:	The variance between subjects or units of randomization may be controlled in part by stratification. In a cluster randomized trial, the between-cluster variation is reduced if like clusters are first matched to form strata. Clusters may be matched on known characteristics such as demographics, location, and number of full-time employees. When the number of clusters is small, creating groups by matching multiple domains may not be feasible. An oft recommended matching variable is based on the study outcome as measured at baseline. This may serve well as a proxy for other potential matching variables. Stratification derived from baseline outcome measures is subject to additional sampling variation. We investigate this source of error in terms of variance components (between and within clusters), intra-cluster correlation, and pre-post correlation.

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