Of key interest were effects involving lifetime MDD status. Figure 2 illustrates that a main effect of lifetime MDD emerged (F(1, 302) = 4.7, p = .03) that was qualified by a lifetime MDD by reference interaction (F(3, 906) = 22.2, p < .001), and supplemental full factorial mixed models performed separately for each reference montage indicated that a main effect of lifetime MDD emerged for CSD (p < .001 and d = .93), demonstrating that the lifetime MDD+ group displayed relatively less left frontal activity than the MDD- group. In contrast, no effects of lifetime MDD emerged for AVG (p > .06), Cz (p > .26), or LM (p > .43). No lifetime MDD by sex or lifetime MDD by sex by reference interactions emerged for the omnibus analysis (both p > .29). In addition, no lifetime MDD by channel or lifetime MDD by channel by reference interactions emerged (both p > .92), indicating that the lifetime MDD effect was not differentially manifest across the four frontal sites.
