Validity and reliability of the Vigour Assessment Scale and an invigoration task in remitted but avolitional schizophrenia

Abstract

In the first empirical study on vigour outside an occupational context, this study examined the validity and the reliability of the Vigour Assessment Scale (VAS) in patients with remitted but avolitional schizophrenia. The validity and the reliability of an imagery-cognitive invigoration task were also examined. The scale and the invigoration task provide means by which to address, scientifically and clinically, the lack of vigour that underpins avolition in schizophrenia, which is a common problem persisting after acute episodes and contributing to marked impairment in socio-occupational functioning. Avolition often responds poorly to treatment and defies other treatment targets that are dependent on vigour. The vigour of 242 outpatients was assessed on the VAS alongside assessments of workplace vigour, behavioural inhibition and activation, procrastination, fatigue, anxiety, depressive features, and active involvement in growing as a person. Patients furthermore participated in an invigoration task (n=76) that was repeated a month later (n=70) for the examination of its effect in a proof-of-concept quasi-experimental one-group sequentially-repeated pre-test/post-test study design. Validity of the VAS was observed in its concurrence with existing instruments of similar kind and its discriminant ability to discern vigour from dissimilar constructs. Concurrence was observed in moderate to strong correlations (r=-0.5 to 0.72) between the VAS and measures approximate to vigour. Discriminant validity was supported by statistically highly significant differences (p<0.001 to 0.003) between the VAS and measurements of procrastination, fatigue, depression, behaviour inhibition and activation, personal growth and initiative, and anxiety. Reliability of the VAS was observed in its internal consistency, split-half reliability, test-retest reliability and standard error of measurement. An exploratory factor analysis yielded six factors, being Task Drive, Indecisiveness, Creative Efforts, Social Disinterest, Active Mobilisation and Torpidity. Internal consistency was excellent with Cronbach alpha coefficients all above 0.8. Split-half reliability testing resulted in a strong correlation between halves (r>0.8). Reliability was further supported by a strong correlation (r=0.8) between initial and repeat VAS measurements. The VAS consistently produced a small standard error of measurement (5.38 or less within a total score range of 77). Validity of the invigoration task was supported by statistically significant differences in VAS scores before and after the two occasions when the task was performed (p<0.001). The effect sizes indicated that the task produced changes that were of a medium (d=0.51) to very large extent (d=1.64). The reliability of the task was supported by its having this effect on two occasions a month apart. The VAS now provides an instrument to assess vigour for diagnostic and therapeutic purposes. Although validated in schizophrenia, it may also prove useful in other clinical or healthy populations, subject to further validation. The proof of concept for the invigoration task warrants a subsequent randomised controlled trial to establish its efficacy by controlling for potential confounding influences. Once established as efficacious in this and other populations, the task holds potential for augmenting standard services and targets in schizophrenia, other clinical populations for whom vigour may be a sensible treatment target, and non-clinical populations affected by burnout or who wish to enhance their vigour as a virtue.