Traitedness is typically examined in personality research as a potential moderator of critical trait-behavior relationships (Tellegen, Kamp, & Watson, 1982) under the assumption that such relationships will only be strong for individuals who truly appear to manifest the trait. For example, in the context of alcoholism research, the extent to which traitedness on a core dependence indicator moderates the relationship between dependence severity and important variables such as treatment outcome and differential treatment response can be examined. Excluding alcohol users who have exhibited some severe alcohol-related behaviors, yet have not followed the normative developmental course, may eliminate ‘noise’ from alcohol diagnostic data and increase power to find matching effects. Such noise might occur by the inclusion of individuals who have a lot of problems consequent to alcohol use (e.g., occupational, social, and legal problems) even though they do not manifest the more severe symptoms of alcoholism (e.g., withdrawals). Thus, IRT is well equipped to operationalize Jellinek’s idea that severity can be reliably defined by one’s position on a developmental course, and it also provides empirical strategies to assess an individual’s
