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Removing facial features from structural MRI images biases visual quality assessment

Table 1

Sensitivity analyses for rm-ANOVA and LME comparisons.

We determined that our rm-ANOVA modeling would confirm differences in manual ratings of f = 0.218 or larger with G*Power [33]. This sensitivity corresponds to = 0.045 (i.e., a medium effect size) following Equation A in S1 Text. In the rm-ANOVA sensitivity analysis, we set two groups (defaced/nondefaced) and four measurements (4 raters) with a total sample size of 185 subjects from the HH site, 90% power, α = 0.02, a nonsphericity correction of 0.34, and a correlation among repeated measures of 0.1. Note that this sensitivity analysis is conservative as we expected a much higher correlation among repeated measures, which would reduce the detectable effect size. Remaining conservative, we iteratively tried different non-sphericity correction values and kept the lowest one possible to maximize the detectable effect size. With G*Power (Fig K in S1 Text), we also estimated the noncentrality parameter λ associated with the likelihood ratio test, which is a proxy for the effect size, yielding λ = 13.017. The degrees of freedom of the likelihood ratio test correspond to the difference in parameter count between the two nested LMEs compared (see Table F in S1 Text).

doi: https://doi.org/10.1371/journal.pbio.3003149.t001