Methods: A total of 115 patients completed the EORTC core questionnaire QLQ-C30 (version 3) after radiotherapy. The
observed response scores, assumed to be one-dimensional, were summed and transformed into expected scores
using the Rasch rating scale model with WINSTEPS software. A series of simulations was performed using a unified
bootstrap procedure after manipulating scenarios with different questionnaire lengths and patient numbers to
estimate the reliability at 95% confidence intervals. Skewness analyses of the 95% CIs were compared to detect
different effects between groups according to the two data sets of observed and expected response scores.