Why we need a better measure of acceptance: development and initial validation of the Southampton Acceptance Sale

Abstract

Acceptance is an important construct across models for understanding psychological distress. Several measures have been designed to capture acceptance, however, there is a lack of evidence regarding the most suitable tool. A systematic review evaluated 20 articles, reporting 32 studies, examining acceptance questionnaires. The methodological quality of included studies were evaluated using the COnsensus-based Standards for the selection of health status Measurement INstruments (COSMIN) checklist. The quality of measurement properties were evaluated using criteria suggested by Terwee et al. (2007). All studies were independently reviewed by two raters, and inter-rater reliability was high. Nine instruments were identified: two unidimensional scales of acceptance, four mindfulness tools with an acceptance subscale, and three emotion regulation scales with an acceptance-based subscale. None of the measures evaluated can be recommended as having superior psychometric properties. Further research is required to demonstrate the psychometric properties of existing measures, given their significant role in evaluating acceptance-based interventions across clinical and research settings.

The lack of a valid and reliable measure of acceptance prevents researchers from drawing conclusions about the efficacy of acceptance-based interventions and identifying the role of acceptance processes in clinical change. Given that there is no current gold standard assessment tool for measuring acceptance, the present study sought to develop and evaluate a new instrument to meet this need. Across three separate studies an initial item pool was evaluated and refined. The resultant measure, named the Southampton Acceptance Scale (SAS), was then evaluated with regards to the factor structure, reliability, and validity. An initial exploratory approach was employed as a unique pool of items with many potential relationships was under investigation. These analyses were subsequently followed up with confirmatory approaches. The SAS, comprising 18-items, was shown to have a theoretically coherent two-factor structure which was validated in an independent sample. The scale has excellent internal consistency, and demonstrated convergent, concurrent and discriminant validity. The SAS has strong psychometric properties and is a promising new measure of acceptance.

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ORCID for Claire Hart: orcid.org/0000-0003-2175-2474

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