253 – Contributed Oral Poster Presentations: Biometrics
Sample Size Calculation for Survival Time Data in Cluster Randomized Trials Using NIATx 200 as an Example
Antje Jahn-Eimermacher
University Medical Center, Mainz
Dennis McCarty
Oregon Health and Science University
Andrew Quanbeck
University of Wisconsin-Madison
Jim Robinson
University of Wisconsin-Madison
In several trials with a time to event endpoint, the interventions to be compared are randomized not to individuals but to groups of individuals (clusters), which might be patients of the same hospital. One example is the NIATx 200 trial, a cluster randomized trial investigating methods of disseminating quality improvement to addiction treatment centers in the U.S.. One of the primary endpoints to be compared between the different interventions is the time patients have to wait for their first treatment. Members of the same cluster tend to be more similar than members of different clusters causing intra-cluster correlation. Correlation affects the power of a trial and thus has to be considered when planning the sample size. We illustrate how to plan the sample size for clustered time to event data using the NIATx 200 trial as an example.
