The Impact of Patient Aggression on Carers Scale: instrument derivation and psychometric testing.

Patient aggression towards carers constitutes a problem for patients and carers alike. Patients' aggressive behaviour often leads to adverse consequences for carers, especially nurses. Various extensive instruments have been developed to measure such adverse effects on carers. The 'Impact of Patient Aggression on Carers Scale' (IMPACS) is a short instrument intended for use in monitoring negative consequences of such incidents. The items of the IMPACS were derived basically from a review of the literature on negative effects of patient aggression on nurses. The IMPACS was administered to a convenience sample of nurses working on 14 psychiatric acute admission wards in the German speaking part of Switzerland. Factor analysis led to the exclusion of three of the original items and to an interpretable three-factor solution with all factors demonstrating eigen values higher than 1. The factors demonstrate moderate to good internal consistency. Canonical correlation analysis using the dimensions of the Maslach Burnout Inventory (MBI) produced a correlation coefficient of 0.457, thus demonstrating external reliability. In spite of some caveats such as possible response bias and the necessity of the investigation of the test-retest stability of the scale this study suggests that the IMPACS is a good measure of adverse effects and thus merits further development.