Harper et al 1 found completion rates and success scaling rates of the St George’s Respiratory Questionnaire (SGRQ) lower than those observed in other questionnaires completed by patients with COPD attending an outpatient clinic. Readers may infer from this finding that the SGRQ is a less useful instrument than the Chronic Respiratory Questionnaire (CRQ), but an alternative explanation may lie on some methodological limitations of the study.

Firstly, the CRQ was administered only to an opportunistic subsample and, unfortunately, the authors provide insufficient information to rule out systematic differences with the rest of the patients. Secondly, the claim that SGRQ had lower completion rates may reflect the local condition in which it was applied rather than a general limitation. The CRQ was administered by an interviewer while the SGRQ …