Inconsistency of findings due to low power: A structural MRI study of bilingualism

Research on structural brain differences between monolinguals and bilinguals remains inconsistent, and this has been proposed by some to be due in part to inadequate sample sizes. The aim of the present study is to reveal the expected degrees of uncertainty among neuroimaging findings by analyzing random samples of varying sizes from a larger-than-average sample. Bilinguals (n = 216) were compared with monolinguals (n = 146) using grey matter volume measures across region-of-interest tests. Variability among findings were compared with the true full-sample findings, and taken in the context of expected differences within the larger bilingualism neuroimaging literature. Results demonstrate excessive variability across the lowest sample sizes (e.g. samples totaling 20-80 participants), and this is explored through the trends of subsample outcomes and effect sizes across sample sizes. The results of this study illustrate the influences of power on expected variability among sample findings.