Irritable Bowel Syndrome Clinical Trials: Getting the IBS-SSS Responder Rates Right

The Irritable Bowel Syndrome – Severity of Symptoms Scale (IBS-SSS) is commonly used in clinical trials with IBS patients to characterize treatment effects. Calculations of responder rates using the data from changes of the IBS-SSS measures commonly use a minus 50 points cut-off value. The present study analyzed data from a recently published IBS-trial with 201 patients to evaluate if this cut-off value is appropriate or needs to be revised. A receiver operating characteristic (ROC) curve for IBS-SSS change data was established using IBS-AR data as a binary classifier. The area under the curve (AUC) and its 95% confidence interval (CI) for the ROC were determined. Curves plotting accuracy rates and Youden’s J index values against changes on the IBS-SSS used as cut-off values were analyzed for maxima to determine the optimal cut-off value for responder rate calculations. The AUC of the ROC curve was 0.9738 with a 95% CI ranging from 0.9565 to 0.9912. The curve of accuracy rates had two maxima (minus 122 and minus 133 points), while that of the Youden’s J indexes had only a maximum at minus 122 points, considered to be the optimal cut-off value for calculating responder rates. The frequently used minus 50 points cut-off value might not be optimal for determining meaningful responder rates from IBS-SSS measurements. At least for the IBS-SSS data analyzed in the present study, a minus 122 points value appears to be more appropriate. Interpretation of IBS-SSS responder rates from past or future clinical trials should carefully check for the cut-off values applied for their calculation.