Linear mixed modeling requires measurement invariance, meaning that the same dependent measure must be used across time (Edwards & Wirth, 2009). Consistent with past literature examining repeated measures of anxious-depressed symptoms across different Achenbach forms (e.g., Edwards, Larsson, Lichtenstein, & Kendler, 2011), the items that loaded on both the YASR and ASR anxious-depressed subscale were summed to create the anxious-depressed symptoms composite. Reliabilities for the resulting 15-item scale at ages 23, 26, and 32 (summarized in Table 1) were high, α23 = .90, α26 = .89, α32 = .90.
