Objective: This study assessed the reproducibility, reliability, and validity of the DDQ-15, a 15-item quality of life questionnaire for patients with digestive disorders (Phases I and II). It also assessed the reliability of two modes of administration of the instrument: paper versus computer (Phase III).
Data Sources/Study Setting: Digestive Disease Center (DDC) patients at the Medical University of South Carolina participated in the study. These patients were attending the DDC on an outpatient basis for a pancreatobiliary disorder, GI cancer, a luminal GI disorder, or liver disorder.
Study Design: Over 200 patients participated in the validation study (Phase II) of the DDQ-15. They completed the instrument three times: within one week before a scheduled clinic visit, at the clinic visit, and approximately two months after the clinic visit. The patients also completed the SF-36 and Gastrointestinal Quality of Life Index during the clinic visit. For Phase III, 150 participants were randomized to take the DDQ-15 on computer first or on paper fist. All participants took both versions during the same clinic visit and prior to being seen by a physician.
Data Collection Methods: Patients responded to the DDQ-15 items directly on the personal computer for the computer version. The paper version was self-administered by the patients, or if they could not read, the responses on the paper version required manual data entry by the study staff.
Principal Findings: For the validation study (Phase II) Cronbach's alpha for the DDQ-15 was 0.92 indicating high internal consistency of the instrument. The intraclass correlation coefficient between pre-clinic and clinic visit scores was 0.97. Pearson's correlation coefficient between the clinic visit DDQ-15 and the Gastrointestinal Quality of Life Index was 0.84, and the coefficients between DDQ-15 and the subscales of SF-36 ranged from 0.55 to 0.79. For Phase III, high internal consistency was observed for both versions, and reproducibility analysis yielded excellent agreement between the two. Intraclass correlation scores indicated high concordance of DDQ-15 scores. Education level and the order in which the two versions were completed were significant factors affecting the concordance of responses.
Conclusions: DDQ-15 was shown to be a reliable, reproducible, and valid instrument for assessing QOL in patients with digestive diseases. The simplicity of the instrument should facilitate its use in an ordinary clinical setting. The study also showed that agreement between computer and paper DDQ-15 versions was excellent, indicating that mode of administration minimally affected response to QOL items. This study showed the computer interface to be a reliable alternative to the conventional paper questionnaire.