Tetrachoric correlations (for binary phenotypes) and polychoric correlations (for binary and count phenotypes) were calculated using SAS9.4 (SAS Institute Inc. Cary, NC, USA). We conducted an item response analysis in Mplusv833, using a two-parameter logistic model, to confirm the uni-dimensionality underlying the seven criteria and to examine the discrimination and difficulty associated with each criterion (see Supplemental Text).
