We are aware of no previous broad-based analysis of lifetime comorbidity predicting the subsequent first onset of a range of secondary disorders other than our own prior cross-national cross-section study of adults (Kessler et al., 2011). Our finding of largely sub-additive predictive associations of comorbid disorders, which we also found in our adult study, is consequently unique. It is important to note that this sub-additivity is based on a logistic model, though, which means that an additive specification with a linear or other link function might fit the data. However, our efforts to find an alternative link function that provided a better fit of the data with an additive specification was unsuccessful. This sub-additive pattern has potentially important implications for intervention because it suggests that intervening with a single comorbid disorder might not be effective in preventing subsequent disorder onset, as incremental predictive effects of individual disorders decrease with number of other disorders. To the extent that primary disorders are causes, treatment of the entire cluster of comorbid disorders is likely to be more effective than treatment of individual primary
