There is a growing interest to use health status or disease control questionnaires in routine clinical practice. However, the validity of most questionnaires is established using techniques developed for group level validation. This study examines a new method, using patient interviews, to validate a short health status questionnaire, the Clinical COPD Questionnaire (CCQ), at the individual patient level.
Patients with COPD who visited an outpatient clinic completed the CCQ before the consultation, and the specialist physician completed it after the consultation. After the consultation all patients had a semi-structured in-depth interview. The patients' CCQ scores were compared with those of the treating clinician, and with mean scores from 5 clinicians from a pool of 20 who scored the CCQ after reading the transcript of the in-depth interviews only. Agreement was assessed using Lin's concordance correlation coefficient (CCC), and Blant and Altman plots. Interviews with patients with low agreement were reviewed for possible explanations.
A total of 44 COPD patients (32 male, mean age 66 years, FEV1 45% of predicted) participated. Agreement between the patients' CCQ scores and those of the treating clinicians (CCC = 0.87) and the mean score of the reviewing clinicians (CCC = 0.86) was very high. No systematic error was detected. No explanation for individuals with low agreement was found.
The validity of the CCQ on the individual patient level, as assessed by these methods, is good. Individual health status assessment with the CCQ is therefore sufficiently accurate to be used in routine clinical practice.