Validation of a 7-point Global Overall Symptom scale to measure the severity of dyspepsia symptoms in clinical trials
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BACKGROUND: Currently there is no consensus on the optimal method to measure the severity of dyspepsia symptoms in clinical trials. AIM: To validate the 7-point Global Overall Symptom scale. METHODS: The Global Overall Symptom scale uses a 7-point Likert scale ranging from 1 = no problem to 7 = a very severe problem. Validation was performed in two randomized-controlled trials (n = 1121 and 512). Construct validity: Global Overall Symptom was compared with the Quality of Life in Reflux And Dyspepsia, Gastrointestinal Symptom Rating Scale, Reflux Disease Questionnaire and 10 specific symptoms using Spearman correlation coefficients. Test-retest reliability: The Intraclass Correlation Coefficient was calculated for patients with stable dyspepsia defined by no change in Overall Treatment Effect score over two visits. Responsiveness: effect size and standardized response mean were also calculated. RESULTS: Construct validity: Change in Global Overall Symptom score correlated significantly with Quality of Life for Reflux And Dyspepsia, Gastrointestinal Symptom Rating Scale, Reflux Disease Questionnaire and specific symptoms (all P < 0.0002). Reliability: The Intraclass Correlation Coefficient was 0.62 (n = 205) and 0.42 (n = 270). Responsiveness: There was a positive correlation between change in Global Overall Symptom and change in symptom severity. The effect size and standardized response mean were 1.1 and 2.1, respectively. CONCLUSION: The Global Overall Symptom scale is a simple, valid outcome measure for dyspepsia treatment trials.
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