Measuring Change in Symptoms of Neurobehavioural Disability: Responsiveness of the St Andrew's-Swansea Neurobehavioural Outcome Scale

Abstract

Objective: Neurobehavioural disability (NBD) after acquired brain injury (ABI) is often associated with poor outcome. The "St Andrew's-Swansea Neurobehavioural Outcome Scale" (SASNOS) was developed to measure NBD in a range of applications. Two of the "holy trinity" of psychometric properties, reliability and validity, have been comprehensively mapped, but the extent to which SASNOS meets the third, responsiveness, has not been investigated. Demonstrating responsiveness is essential in instruments employed in repeated measurement scenarios to confirm their ability to discriminate real change from error. However, there is no single agreed method for determining responsiveness. For some instruments, this property remains unexplored. A difference in scores attaining statistical significance for aggregate data is frequently cited as support for this construct, but this approach remains heavily criticized. This study explores responsiveness of SASNOS.

Method: Consecutive SASNOS assessments completed over varying times for 145 individuals participating in neurobehavioural rehabilitation, drawn from multiple services, were compiled into a retrospective sample of convenience. Multiple methods were employed to confirm internal responsiveness, including those identifying statistically significant change, minimally detectable change and minimally important change.

Results: All methods confirmed responsiveness as a psychometric property of SASNOS; the extent depended on method used and NBD domain investigated. A number of indicators are presented, which equip clinicians and researchers with options to interpret results from repeated assessments, including the individual level in the context of rehabilitation.

Conclusions: SASNOS reliably measures change over time in NBD symptoms, further confirming its suitability as an instrument for investigating multidimensional outcomes of ABI.

Keywords: Assessment; Head injury, traumatic brain injury; Norms/normative studies; Practice effects/reliable change; Rehabilitation; Statistical methods.