A measure less commonly used to quantify P3 amplitude, but that may capture more P3 variance than does the peak, is to take the mean within some latency window. Therefore, we performed follow-up analyses using the mean amplitude within a latency window that was centered on each individual subject’s peak P3 amplitude. A 40 ms window was chosen to capture more P3 variance than does the peak, while excluding potential influence from earlier or later ERP activity. In the univariate probit regression model, mean P3 amplitude accounted for slightly more variance in group membership than did peak P3 amplitude for all diagnostic groups except DAD, for which it accounted for slightly less variance (differences between pseudo-R2 for P3 peak and P3 mean were all .01 or less; see Table 3). In the bivariate model with TF component PC3, results using mean P3 closely agreed with those using peak P3: PC3 still accounted for significant variance above and beyond that accounted for by P3 across diagnostic groups (again, not quite significant for DAD; see Table 4).
