Fig. 1

Comparison of the matched vs. non-matched groups on the covariates. Although no ideal match was attained on all covariates, the match between the groups was substantially improved. Note: The standardized mean difference (SMD) indicates the extent to which the groups differ on a given covariate; smaller values are desired. The highlighted vertical line at .1 indicates the recommended maximum SMD. For information regarding how the background variables were assessed, see Table 1