Due to the inherent differences in the two domains of literature, simple counts were obtained to calculate one odds ratio (OR) for each study. The OR was chosen as the best effect size since both variables (parent information and disorder diagnosis) were dichotomous (Lipsey & Wilson, 2001). One advantage of using the OR is its equivalence across all studies, regardless of the literature domain (PAE vs COA), different covariates collected and utilized across studies, or type of sample (twin study vs ascertained sample). For each study, simple counts were entered into a 2 (prenatal alcohol exposure/AD parent = yes or no) × 2 (disorder diagnosis = yes or no) table in the “2 by 2 frequency table” option in the Practical Meta-Analysis Effect Size Calculator (David B. Wilson, Ph.D., George Mason University, http://www.campbellcollaboration.org/resources/effect_size_input.php). The website provided the OR, a 95% confidence interval (CI), natural log of the OR, and the variance of the natural log of the OR, among other statistics. Numbers for the 2×2 frequency table were based on (1) tables or counts in published studies, and (2) percentages or proportions reported.
