To develop a measure of disease-specific health-related quality of life for achalasia for use as an outcome measure in clinical trials.
We generated a list of potential items for a measure of disease-specific health-related quality of life for achalasia by semistructured interviews with seven persons with achalasia, and by expert opinion. We then used factor analysis and item response theory methods for item reduction, using responses on the long-form questionnaire from 70 persons with achalasia. The severity measure underlying the item responses was constructed using a Rasch model.
We developed a 10-item measure of disease-specific health-related quality of life that sampled the concepts of food tolerance, dysphagia-related behavior modifications, pain, heartburn, distress, lifestyle limitation, and satisfaction. The measure was reliable (person separation reliability 0.79, Cronbach's α 0.83), showed evidence of construct validity and good data-to-model fit (mean infit and outfit statistics for items, 1.00 and 0.98, respectively), and had a wide effective measurement range (able to discriminate between 87% of subjects with achalasia). The measure was recalibrated onto a 0–100 interval-level scale.
We describe a reliable measure of achalasia disease-specific health-related quality of life that has a broad effective measurement range, interval-level properties, and evidence of construct validity. This measure is appropriate for use as an outcome measure in clinical trials and other evaluative studies on the effectiveness of treatment for achalasia.