
6
Sample Size Determination for Correlated
Outcomes from Three-Level Randomized
Clinical Trials
6.1 Introduction
We now consider sample size approaches for randomized clinical trials with
a three-level data structure. One example of a study with this structure is a
large scale randomized trial to test a behavioral intervention to increase phys-
ical activity in school age children. In this design, students (level 1) are nested
within classrooms (level 2) which are nested within schools (level 3). A second
example is a longitudinal study of patients from multiple clinics in which the
repeated measures comprise the first level, patients are the second lev ...