Abstract
ObjectiveResults of epidemiological studies are greatly influenced by the chosen methodology. The study aims to investigate how two frequently used questionnaires (Qs), with partly different layout, influence the prevalence of respiratory symptoms.Study Design and SettingA booklet containing two Qs, the Global Allergy and Asthma European Network Q and the Obstructive Lung Disease in Northern Sweden Q, was mailed to 30 000 subjects aged 16–75 years in West Sweden; 62% responded. Sixteen questions were included in the analysis: seven identical between the Qs, four different in set-up and five with the same layout but different wording. Comparisons were made using differences in proportions, observed agreement and Kappa statistics.ResultsIdentical questions yielded similar prevalences with high observed agreement and kappa values. Questions with different set-up or differences in wording resulted in significantly different prevalences with lower observed agreement and kappa values. In general, the use of follow-up questions, excluding subjects answering no to the initial question, resulted in 2.9–6.7% units lower prevalence.ConclusionThe question set-up has great influences on epidemiological results, and specifically questions that are set up to be excluded based on a previous no answer leads to lower prevalence compared with detached questions. Therefore, Q layout and exact wording of questions has to be carefully considered when comparing studies.Please cite this paper as: Ekerljung L, Rönmark E, Lötvall J, Wennergren G, Torén K and Lundbäck B. Questionnaire layout and wording influence prevalence and risk estimates of respiratory symptoms in a population cohort. Clin Respir J 2013; 7: 53–63.
Highlights
Postal enquiries are among the most efficient tools when assessing prevalence and risk factors of asthma and respiratory symptoms [1, 2]
The response rate was 62% higher among women compared with men [67.4% vs 56.4%] (Table 1)
Prevalence of reported ‘physician-diagnosed chronic obstructive pulmonary disease (COPD)’ was 3.2% using the Obstructive Lung Disease in Northern Sweden Q (OLIN-Q) vs 1.4% using GA2LEN-Q and ‘rhinorrhea’ was 14.9% vs 6.1%
Summary
Postal enquiries are among the most efficient tools when assessing prevalence and risk factors of asthma and respiratory symptoms [1, 2]. The prevalence of asthma has increased over the last 50–60 years and is estimated to be 7%–10% in different parts of the Western world [3,4,5,6]. Data on incidence vary partly depending on different definitions of asthma and population at risk. Two main models have been used in the validation of epidemiological diagnosis of asthma: a provocation test or a clinical interview [1, 2, 11], or a combination of both methods [12]
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