In this commentary, we clarify the meaning of the generalizability-theory-based coefficients reported in our multisite reliability study of fMRI measures of regional brain activation during an emotion processing task (Gee et al., Human Brain Mapping 2015;36:2558-2579). While the original paper reported generalizability and dependability coefficients based on the design of our traveling subjects study (in which each subject was scanned twice at each of eight sites), those coefficients are of limited applicability outside of the reliability study context. Here we report generalizability and dependability coefficients that represent the reliability one can expect for a multisite study, in which a given subject is scanned once on a scanner drawn randomly from the pool of available scanners (i.e., analogous to the more typical multisite study design). We also characterize the implications of a multisite versus single-site study design for statistical power, including Figure 1 that shows sample size requirements to detect activation in two key nodes of the emotion processing circuitry given observed differences in reliability of measurement between single-site and multisite designs.
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