Lahey, Benjamin B., and Irwin D. Waldman: Developmental Propensity Model

Developmental Model

In their model, Lahey and Waldman integrate the developmental aspect of Moffitt's dual taxonomy theory. Their model differs from Moffitt's, however, in terms of both the age of onset and the causal influences on conduct problems. First, Moffitt views age of onset as a dichotomous variable, that results in two distinct developmental trajectories for youths with conduct problems (i.e., adolescent-limited and life-course-persistent). On the other hand, Lahey and Waldman, argue that the age of onset varies along a continuum rather than a true dichotomy, resulting in multiple developmental trajectories for conduct problems. Second, Moffitt's theory asserts that the causal processes are different for the two categories of antisocial youths. In contrast, Lahey and Waldman contend that the underlying causes of conduct problems are the same regardless of the age of onset. Rather they argue that it is the strength and pattern of the causal influences that vary based on the age of onset.

As mentioned, Lahey and Waldman's model seeks to explain the various developmental trajectories of conduct problems in youths. The first step in accomplishing this is to distinguish between two types of conduct problems: developmentally early and developmentally late conduct problems. First, developmentally early conduct problems are actions that are seen as fairly “normal” in young children and tend to become less prevalent as the youth enters his or her teenage years. Examples of developmentally early conduct problems include lying and minor forms of aggression such as bullying, fighting, and hurting animals. On the other hand, developmentally late conduct problems encompasses nonaggressive forms of conduct problems, such as stealing, breaking and entering, running away from home, and truancy as well as serious forms of aggression, such as rape, use of a weapon, and mugging. These types of behaviors are rare in early childhood and tend to emerge in late childhood and peak during adolescence.

Lahey and Waldman argue that there is considerable variation in the initial levels of developmentally early conduct problems in children at school entry age (i.e., intercept). The slopes (i.e., rate of change over time) can then vary in all possible directions from these initial start points. For example, two youths may have the exact same level of developmentally early conduct problems at school age, but based on their respective antisocial propensities and interactions with their environments, one youth may persist/worsen over time while the [Page 541]other may desist. Lahey and Waldman propose several hypotheses related to the developmental trajectories of conduct problems in adolescence based on an individual's level of developmentally early conduct problems at school entry. For example, youths who have high initial levels of developmentally early conduct problems at school entry are more likely (1) to continue exhibiting conduct problems, often to a higher degree, and are less likely to desist over time and (2) to demonstrate their developmentally late conduct problems at an earlier age and at a higher rate once they reach adolescence.

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