Validity and the minimum important difference of the chronic respiratory disease questionnaire in people with interstitial lung disease

Interstitial lung disease (or ILD) are a disabling group of chronic lung conditions associated with interstitial inflammation and fibrosis to the lung tissue. People with ILD often suffer from dyspnoea, fatigue, anxiety, depression, cough, and reduced exercise tolerance. These symptoms are often debilitating and have a significant impact on the patient's health-related quality of life (HRQOL). Patient-reported outcomes (PROs), directly provided by patients on their perceived health status, are important for assessing the impact of disease and the effect of interventions. Two disease specific questionnaires, the Chronic Respiratory Disease Questionnaire (CRQ) and the St. George's Respiratory Questionnaire (SGRQ), are used most often to assess the HRQoL in people with ILD. Both the CRQ and SGRQ have been used successfully in trials evaluating pulmonary rehabilitation in ILD, demonstrating meaningful improvements in HRQoL. The SGRQ has been validated in ILD and has established estimates of the minimum important difference (MID). The MID is the smallest change in a patient-reported outcome that is important from the patient’s perspective and would warrant a change in a patient’s medical management. The CRQ on the other hand has not been tested for validity and has no established MIDs estimates for people with ILD. This project will aim to determine the validity and the minimal important difference of the CRQ in people with ILD. This project will involve a secondary analysis of baseline, post intervention and 6 months clinical outcome data collected from our earlier randomised controlled trial examining the effects of exercise training in people with ILD on HRQOL.