The LCQ is a cough specific quality of life questionnaire with 19 items. It is designed for self-administration and takes less than 5 minutes for completion. The 19 items are divided into 3 domains: physical, psychological and social. A 7-point Likert scale is used to evaluate the answers; a higher score indicates a better health status. The total score is the sum of the scores of the three domains (varying 1 to 7). The LCQ already has been validated in English and has also been used in at least one other language1113.

All patients with chronic cough referred to our tertiary cough clinic between May 2004 and February 2005 were asked to participate by completion of the questionnaires at the first visit, after 2 weeks and after 6 months. Chronic cough was defined as a cough lasting more than 8 weeks that remained unexplained after assessment by the primary care physician.

We used the LCQ, the Short Form36 (SF36), a generic quality of life questionnaire14, the Hospital Anxiety and Depression Scale (HADS), a questionnaire to detect mild forms of depression and anxiety15, a modified Borg score for cough scoring the intensity on a scale from 0 (no cough at all) to 10 (maximum cough) and a questionnaire to quantify the degree of change in cough (global rating of change: GRC). The GRC assessment was done to evaluate self-perceived changes in disease control since the first visit. Responses were scored from +7 (a very great deal better) to -7 (a very great deal worse); 0 indicated no change. Scores of -3, -2, +2 and +3 were considered to represent minimal but nevertheless clinically important changes. 16.

The translation followed an established forward-backward translation procedure, with independent translations and counter-translation. Independent translations into Dutch of the LCQ (the authors J.B and A.H) were pooled to a common version. A native English speaker fluent in Dutch and with a medical background translated this provisional Dutch version back into English. This back translation was found to be nearly identical to the source document. The Dutch version [see Additional file] was then tested in 4 patients with chronic cough for problems in acceptance and comprehension of the questionnaire content or the phrasing.

To validate the LCQ we tested four different aspects of the questionnaire, i.e. the concurrent validity, the internal consistency, the repeatability and the responsiveness. The first two aspects are related to validity, the instrument's ability to measure what it purports to measure17. Concurrent validity was tested by comparing the LCQ with other health outcome questionnaires during the first visit. The internal consistency, the degree of homogeneity within a domain, was determined by the degree of correlation between the answers on the questions within a domain.

The repeatability (or test-retest reliability) measures the stability of scores on the LCQ over time. In our patients repeatability was determined by comparing the LCQ scores of the first visit with the LCQ scores after 2 weeks in patients who reported their cough had been unchanged (GRC score = 0).

Responsiveness of a test is the capacity to detect important changes over time18. In our study responsiveness was determined by comparing the LCQ scores between the first visit and the LCQ scores after 6 months in patients who told their cough had significantly improved (GRC = 4)

SPSS version 12 was used for data analysis. Data are presented as mean (SE) or ranges. Pearson correlation coefficients between LCQ scores and the scores of the other health outcome were used to determine concurrent validation. Internal consistency was determined by calculating the Cronbach's alpha coefficients for the three domains and the total LCQ. Analysis of the test-retest reliability was done by calculating the Intraclass Correlation Coefficient (ICC) for the three domains and for the total score. Responsiveness was analysed by calculating the 95% confidence interval for the average improvements in the three domain scores and the total score of the LCQ.

The patients' characteristics are shown in table 1. The majority of the patients were female, of middle age.

The correlation coefficients of the concurrent validity, determined in 152 patients, are shown in table 2. Except for two all outcome are statistically significant. Summarised, the correlation coefficients with the Borg Cough Scale, the SF-36 general health and the HAD total score were respectively -0.41, 0.41 and -0.46.

The Cronbach's alpha coefficients for the physical, psychological, social domains and for the total questionnaire were 0.77, 0.84, 0.83 and 0.93 respectively. A Cronbach's alpha coefficient >0.7 is generally accepted as good.

The intraclass correlation coefficient (ICC) of the test-retest reliability was 0.93 for the total score. In table 3 the ICCs are shown for the domains and the total score. In addition, the results of the original LCQ are shown.

The LCQ scores improved significantly after treatment. Results are shown in table 4.