Observed (O) and expected (E) prevalence (%) of exposure to increasing number of adverse childhood experiences and observed-to-expected ratio by parental educational level.

P values were the same (p2 test with 3 degrees of freedom testing the null hypothesis of no differences in the observed and expected frequencies across all number of ACE categories. Given the prevalence of the risk factors within each group and on the basis of the assumption that all of the ACEs were independent of each other. The between-group comparison used the expected value from the total number of individuals as comparison.