Psychometric evaluation of the 10-item Short Opiate Withdrawal Scale-Gossop (SOWS-Gossop) in patients undergoing opioid detoxification.

INTRODUCTION The Short Opiate Withdrawal Scale (SOWS)-Gossop is a 10-item questionnaire developed to evaluate opioid withdrawal symptom severity. The scale was derived from the original 32-item Opiate Withdrawal Scale in order to reduce redundancy while providing an equally sensitive measure of opioid withdrawal symptom severity appropriate for research and clinical practice. The objective of this study was to examine the psychometric properties and provide score interpretation guidelines for the SOWS-Gossop 10-item version. METHODS Blinded, pooled data from two trials assessing the efficacy of lofexidine hydrochloride in reducing withdrawal symptoms in patients undergoing opioid detoxification were used to evaluate the quantitative psychometric properties and score interpretation of the SOWS-Gossop. RESULTS Five hundred fifty-five (N=555) observations were available at baseline with numbers decreasing to n=213 at day 7. Mean (standard deviation) SOWS-Gossop scores were 10.4 (6.86) at baseline, 8.7 (6.49) on day 1, 10.5 (7.21) on day 2, and 3.1 (3.95) on day 7. Confirmatory factor analysis indicated that the SOWS-Gossop items loaded on a single factor consistent with a single total score. Intra-class correlations (95% confidence interval) were 0.78 (0.70-0.85) between baseline and day 1, 0.84 (0.79-0.89) between days 4 and 5, and 0.88 (0.83-0.91) between days 6 and 7, demonstrating good test-retest reliability. Mean SOWS-Gossop scores varied significantly (p<0.0001) by Modified Clinical Global Impression severity groups supporting known-groups validity. Most correlations with conceptually similar instruments were over 0.4, providing evidence of construct validity. Results suggest that a change score of approximately 2-4 points is likely a small but meaningful improvement on the SOWS-Gossop Total Score. CONCLUSIONS The findings of this study indicate that the SOWS-Gossop includes concepts that are relevant to patients' experiences with opioid withdrawal and has excellent psychometric properties. The SOWS-Gossop is an appropriate, precise, and sensitive measure to evaluate the symptoms of acute opioid withdrawal in research or clinical settings.