Unidimensionality of the Strengths and Vulnerabilities Scales in the Short-Term Assessment of Risk and Treatability (START)

The Short-Term Assessment of Risk and Treatability (START) is a 20-item structured professional judgment instrument for assessing dynamic risk in mental health services. Much of the START research literature examines the relationship between Strengths and Vulnerabilities sub-scale total scores and various adverse outcomes including violence. This assumes that the two sub-scales have the psychometric property of unidimensionality i.e. all the items cluster together as a measure of a single construct. Such assumed unidimensionality is a necessary condition for any analyses based on scale "total score" and the widespread use of scores summated in this way in research studies may obscure more specific clusters of items within each sub-scale. This multinational study examined START assessments (n = 685) conducted in four forensic services in Scandinavia and the UK using principal component analysis. It was found that all but three Strengths items (Substance Use, Social Support and Material Resources) and all but four Vulnerabilities items (Substance Use, Social Support, Material Resources and Self care) loaded >0.5 on the expected component. This indicates a unidimensional structure underlying the START and provides empirical support from a large multinational sample for the widespread use of summated Strengths and Vulnerabilities scores in forensic psychiatric risk research.