International assessment of the internal consistency of respiratory symptoms

We aimed to assess cross-cultural validity of the reporting of respiratory symptoms in the European Community Respiratory Health Study (ECRHS). A rand om sample of subjects from the general population (aged 20-44 yr), from 35 centers in 15 countries, answered a questionnaire and underwent allergy tes ts and airway challenge with methacholine. The overall response rate to the questionnaire was 60% (n = 16,635). Exploratory factor analysis was used t o identify how symptoms were grouped (i.e., to specify factor structure), u sing data from the United Kingdom. Subsequently, a confirmatory factor anal ysis of the prespecified structure for the United Kingdom was assessed for each country in consecutive nested models, increasing at each step the numb er of parameters forced to be equal to the United Kingdom, and assessing th e goodness of fit. Variables were clustered in the same four groups (factor s) in all countries. The four factors, mutually adjusted, were associated w ith either bronchial responsiveness, atopy, or smoking, which provides cohe rence for the separation of the four factors. In the confirmatory factor an alysis, when the load of each of the symptoms in the corresponding factor w as prespecified, all countries except Spain showed an adequate fit; in Spai n there were differences in answers concerning asthma treatment. We conclud e that the ECRHS multilingual translated respiratory symptoms questionnaire shows high internal consistency, suggesting that international comparisons are not affected by errors due to cross-cultural variations in the reporti ng of symptoms.