This study had a number of other important limitations. The richness and range of variation in study variables had to be reduced by necessity, in order to preserve confidentiality and avert the possibility of individual identification of subjects (for whom individual informed consent was waived). Furthermore, the question of whether maltreatment occurred before or after the development of externalizing behavior was not resolvable in the current data set because the dates of earliest report of maltreatment werenot consistently available. Our analysis of the effects of birth year, coupled with a recent study of self-report maltreatment and psychopathology from over 3,000 twins and siblings [31] in the ADD Health Study, have suggested that the direction of causation is from maltreatment to abnormal behavior rather than the other way around.
