TL17: How to treat site in clinical trials - fixed or random?
*Chul H Ahn, FDA-CDRH 

Keywords: site-by-treatment interaction, site poolability, variance component

In clinical trials, we often treat site as fixed, and examine graphically the treatment effects across sites and also test for the interaction of site-by-treatment by including the interaction term in the statistical model. However, another option is to treat site as random since it is more natural. Here we test for site-by-treatment interaction using variance component. If there is a significant interaction, then the treatment effect can be estimated from the mixed effect model with both site and site-by-treatment interaction included as random effects. Participants will share their thoughts on this important issue.