All Adverse Childhood Experiences Are Not Equal: The Contribution of Synergy to Adverse Childhood Experience Scores

The operationalization of childhood trauma and adversity into checklists commonly known as adverse childhood experiences, or ACEs, has become the most widely adopted methodology linking traumatic childhoods to adult outcomes. As the number of self-reported ACEs increase from 0 to 4 or more (4+), most studies find a roughly stepwise progression in risk for a wide range of negative medical and mental health outcomes. A score of 4+ ACEs, has become a de facto cutpoint, increasingly used clinically to define "high risk" status for a myriad of outcomes. Comparisons across studies using a 4+ cutpoint, however, find considerable heterogeneity in the degree of risk for the same outcomes. In addition to sample and methodological differences, certain pairs of ACEs comprising the cumulative ACE score interact synergistically to significantly increase the overall risk beyond the sum (or product) of the contributions of each ACE to the outcome. This article reviews the empirical literature on synergistic ACEs including results from a general population adult and a mixed trauma, youth sample both sufficiently powered to examine over 20 different ACE pairings for possible synergy. Synergistic pairs of ACEs vary by gender and age group. About 30-40% of the variance in outcomes is accounted for by additive synergistic interactions between certain pairs of ACEs. Across studies, sexual abuse is the most synergistically reactive ACE. The article concludes with a discussion of the implications of synergistic ACE pairings for psychologists and other allied professionals across clinical practice, prevention, research, and policy. Public Significance Statement This study reviews evidence that an empiric interaction (synergy) between pairs of adverse childhood experiences (ACEs) makes larger than expected contributions to outcomes. Sexual abuse, physical abuse, and neglect are the most synergistic ACEs. The clinical, research, and public policy implications of synergy are discussed.