Instrumental and expressive representations of aggression: One scale or two?

The Expagg questionnaire was developed to measure a subject's view of their own aggression as a relatively instrumental or relatively expressive act. Two issues have been raised pertaining to the dimensional structure of the questionnaire: the use of principal components analysis on dichotomous responses and the possibility that instrumental and expressive representations might be independent dimensions rather than opposite ends of a single continuum. In study 1, dichotomous Expagg data from 405 subjects were subjected to microfact, principal components, and factor analysis. Each produced a first general factor, and the correlations between the item loadings were in excess of r = .99. In study 2, a 40-item Likert scale version of Expagg was given to 295 subjects. Principal components analysis, paired item correlations, and subscale correlations suggested partial independence of instrumental and expressive items. Two new 8-item scales measuring instrumental and expressive representations were constructed that maximise their independence. Potential uses of these revised scales are discussed. Aggr. Behav. 25:435–444, 1999.