The Intraclass Correlation Coefficient (ICC) is well known in psychometry as an index of reliability
46 and has been applied to determine the reliability of the fMRI activation patterns. There are several ICC model alternatives, and this study uses the one-way ANOVA model (
ICC1) that is specifically suitable for this type of fMRI data.
31,33 In this study, only within-subject variance (
σwithin) and between-subject variance (
σbw)) are considered. ICC estimates the proportion of variance that is due to differences between the subjects rather than differences due to the measurements; therefore, it can be described by the following equations 2 and 3. Thus, smaller values of
σwithin result in a higher ICC.
From a computational view, ICC,
σbw and
σwithin are represented by the mean square between
n subjects (MSB) and mean square within subjects (MSW). In equations 4 and 5, index
i represents
ith session, and index
j represents the
jth subject. The symbol
k is the number of total sessions, which is equal to 3. The total subject number,
n, is different in different paradigms due to data that were excluded due to head movement. We applied the ICC analysis on the activation percentage for each lobe of the brain for each paradigm across the three sessions.