¹  In Figures 1 and 2, paths sharing labels are constrained to be equal. Unlabeled paths are constrained to be 1, except the paths marked by an asterisk which are freely estimated. Variances and covariances are represented with double-headed arrows. Variances and covariances not shown are constrained to be 0, except covariances among the residuals for observed M and Y which are excluded from this path model for visual parsimony.