Figure.

Statistical power as a function of sample size across multiple effect sizes (Cohen’s d for one group all correct trials versus rest contrast) for left dorsolateral prefrontal cortex (A) and left superior parietal cortex (B). The red lines represent power for multisite studies while the blue lines represent power for single-site studies, with nominal effect sizes adjusted downward for observed reliabilities in the multisite and single-site contexts, respectively. For DLPFC, although higher levels of power are achieved with smaller sample sizes in the single-site compared with multisite context, multisite studies achieve acceptable levels of power (≥ 0.8) with moderate to large effect sizes (ES ≥ 0.5) beginning at sample sizes of approximately 125 subjects. For PC, where there is no difference between multisite versus single site reliability (and therefore the red and blue lines overlap), power is adequate to detect moderate to large effect sizes (ES ≥ 0.5) beginning at sample sizes of approximately 50 subjects in either the single or multi-side study context.