We used the expectation maximization (EM) algorithm for maximum likelihood (ML) estimation for missing data imputation using SAS (SAS Institute, 2002-2006), after the Little's chi-square test of Missing Completely At Random (MCAR test; Little, 1988) resulted in a non-significant chi-square of 8078.96 (df = 8020), p > .05, indicating that missing values were a random subset of the complete data. Thus, we deemed that the imputed data were unbiased (Little & Rubin, 1987; Schafer, 1997).
