The perils of partialling: cautionary tales from aggression and psychopathy

Although a powerful technique, the partialling of independent variables from one another in the context of multiple regression analysis poses certain perils. The present article argues that the most important and underappreciated peril is the difficulty in knowing what construct an independent variable represents once the variance shared with other independent variables is removed. The present article presents illustrative analyses in a large sample of inmates (n=696) using three measures from the psychopathy and aggression fields. Results indicate that in terms of relations among items on a single scale and relations between scales, the raw and residualized scores bore little resemblance to one another. It is argued that researchers must decide to which construct-the one represented by the original scale or the one represented by the residualized scale-conclusions are meant to apply. Difficulties in applying the conclusions to the residualized scale are highlighted and best practices suggested.     

The Theory of Planned Behavior and Breast Self-Examination: Distinguishing Between Perceived Control and Self-Efficacy

This paper reports an application of the theory of planned behavior (TPB) to the prediction of breast self-examination (BSE) intentions and behavior. The study also considered the distinction between perceived control and self-efficacy within the TPB and the additional predictive utility of past behavior. A sample of 95 women completed questionnaires based on the TPB and were followed up at 1 month. Support for the distinction between perceived control and self-efficacy was provided by principal components analysis. The TPB was found to be highly predictive of intention to perform BSE and subsequent BSE behavior. Regression analyses revealed self-efficacy and attitude to be predictive of intention to perform BSE. Intention, in turn, was the sole predictor of BSE at 1-month follow-up. Past behavior was found to explain additional variance in intention, but not BSE behavior at 1-month follow-up. The results are discussed in relation to the conceptual status of the perceived behavioral control construct, and the practical implications of the results are highlighted.