Validity and reliability of the Vigour Assessment Scale in avolitional schizophrenia outpatients

Abstract

A few items of existing schizophrenia scales measure avolition, but no research has been reported on vigour in schizophrenia, including whether avolition would be more or less the inverse of vigour. Such research requires a valid and reliable measure of vigour. In the absence of this, this study developed and examined the validity and the reliability of the Vigour Assessment Scale (VAS) among 242 avolitional schizophrenia outpatients in relation to measures of workplace vigour, behavioral inhibition and activation, procrastination, fatigue, anxiety, depressive features, and active involvement in personal growth. Convergent validity was found in moderate to strong correlations (r = 0.5 to 0.714) between the VAS and measures approximate to vigour. Discriminant validity was found in lower and/or inverse correlations with depression (r = -0.423), anxiety (r = -0.279), behaviour inhibition (r = -0.045), procrastination (r = -0.656), and fatigue (r = -0.684). Internal consistency was good with Cronbach's alpha coefficients above 0.8, and strong correlations for split-half (r = 0.71) and test-retest (r = 0.77) reliability. The standard error of measurement was seven on a scale of 145 points. An exploratory factor analysis yielded a 27-item version with a six-factor structure accounting for 61.9% of the cumulative variance. These results suggest that the VAS is a valid and reliable instrument in avolitional schizophrenia outpatients, suitable for use in further research on vigour and when vigour is pursued therapeutically or in efficacy studies. Subject to further validation, the VAS may be used in other clinical populations (e.g., in depression) and healthy populations where vigour may be pursued as a desirable attribute.