Continuous, categorical, and time to event cocaine use outcome variables: degree of intercorrelation and sensitivity to treatment group differences

Although a number of cocaine use variables are available for use in treatment outcome studies, there is little information on how strongly these variables are related or their relative sensitivity for detecting treatment group differences. Eight continuous and categorical variables of cocaine use obtained at 6-, 12-, 18-, and 24-month follow-ups, four event history variables, and one summary measure of cocaine use over the 24-month follow-up period were examined. The variables were generally correlated 0.30--0.50 or greater. An exploratory factor analysis in which the repeated measures were averaged across follow-up points yielded two factors, one made up of incidence of use variables (e.g. percent days cocaine use, monetary value of cocaine, abstinence status, time to relapse, urine toxicology) and a second consisting of perceived severity of use variables (e.g. drug and cocaine composites, craving). This factor solution was supported by confirmatory factor analyses conducted at each follow-up point. None of the variables yielded significant differences between the two treatment conditions in the study, standard group and individualized relapse prevention continuing care. However, monetary value of cocaine used and urine toxicology variables yielded the largest effect sizes (eta(2)=0.020 and 0.010, respectively).