Fig 1.

Standardization of image acquisition protocols improves statistical power for multicenter cortical thickness studies. The figure demonstrates a substantive reduction in required sample size when using a standardized image acquisition protocol (orange lines) compared with a nonstandardized protocol (green lines). The solid lines show sample size estimates obtained from conventional power analysis techniques that assume values are sampled from a normal distribution, dashed lines indicate sample size estimates obtained using a nonparametric bootstrap approach.