Background: The Leicester Cough Questionnaire (LCQ) is a valid, reproducible, responsive self-reported cough-specific health status measure. It has been used to assess overall efficacy of treatments for cough, but its threshold for clinical significance, or patient importance, is unknown. The aim of this study was to determine the minimal important difference (MID) of the LCQ for patients with chronic cough; this is the smallest change in quality-of-life score considered to be clinically meaningful.
Methods: The LCQ MID was first estimated by a multidisciplinary panel of experts who reviewed two cases of chronic cough. It was subsequently determined using a standardized method. Fifty-two patients with chronic cough of more than 8 weeks' duration attending a respiratory outpatient clinic were recruited. Participants completed the LCQ at initial evaluation and repeated the LCQ with four Global Rating of Change Questionnaires (GRCQ) more than 2 months later. The LCQ total score ranges from 3 to 21 and from 1 to 7 for physical, psychological and social domains; a higher score indicates a better health-related quality of life. The GRCQ, a 15-point scale scored between +7 (a great deal better) and -7 (a great deal worse), was used to record patient ratings of change in cough symptoms. The MID was defined as the change in LCQ health status corresponding to a small change in the GRCQ score.
Results: The mean (standard deviation) LCQ MID corresponding to a small change in the GRCQ score was 1.3 (3.2); the MIDs for domains were as follows: physical 0.2 (0.8), social 0.2 (1.1) and psychological 0.8 (1.5). This MID for LCQ total score was similar to that determined by the expert panel. The global rating of change scores correlated significantly with the change in LCQ total and domain scores (r=0.4-0.5; p<0.005).
Conclusion: We have demonstrated that the LCQ MID is 1.3. The LCQ MID should aid clinicians and researchers to make meaningful interpretations of health-related quality-of-life data relating to chronic cough.