Questionnaire layout and wording influence prevalence and risk estimates of respiratory symptoms in a population cohort Linda Ekerljung 1 , Eva Rönmark 1,2,3 , Jan Lötvall 1 , Göran Wennergren 4 , Kjell Torén 5 and Bo Lundbäck 1,2 1 Department of Internal Medicine, Krefting Research Centre, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden 2 Obstructive Lung Disease In Northern Sweden (OLIN) studies, Department of Medicine, Sunderby Central Hospital of Norrbotten, Luleå, Sweden. 3 Department of Public Health and Clinical Medicine/Environmental Medicine and Occupation, University of Umeå, Umeå, Sweden. 4 Department of Paediatrics, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden 5 Department of Environmental and Occupational Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Abstract Objective: Results of epidemiological studies are greatly influenced by the chosen methodology. The study aims to investigate how two frequently used question- naires (Qs), with partly different layout, influence the prevalence of respiratory symptoms. Study Design and Setting: A 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. Results: Identical questions yielded similar prevalences with high observed agree- ment 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 answer- ing no to the initial question, resulted in 2.9–6.7% units lower prevalence. Conclusion: The 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 com- paring 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. Key words epidemiology – GA 2 LEN – kappa – OLIN – questionnaire – respiratory symptoms Correspondence Linda Ekerljung, MSc, University of Gothenburg, Krefting Research Centre, Box 424, 405 30 Gothenburg, Sweden Tel: +46 31 786 6715 Fax: +46 31 786 6730 email: linda.ekerljung@gu.se Received: 21 September 2011 Revision requested: 15 December 2011 Accepted: 03 January 2012 DOI:10.1111/j.1752-699X.2012.00281.x Authorship and contributorship Linda Ekerljung participated in the collection of data, performed the statistical analyses and wrote the paper. Eva Rönmark participated in the design of the study and reviewed the manuscript. Jon Lötvall conceived of the study, participated in the design of the study and revised the manuscript. Göran Wennergren participated in the design of the study and revised the manuscript. Kjell Torén participated in the design of the study and revised the manuscript. Bo Lundbäck conceived of the study, participated in the design of the study and helped write the paper. All authors read and approved the final manuscript. Ethics The study has been approved by the regional ethics boards in West Sweden. All study subjects gave informed consent prior to participation in the study. Conflict of interest The authors have stated explicitly that there are no conflicts of interest in connection with this article. Re-use of this article is permitted in accordance with the Terms and Conditions set out at http:// wileyonlinelibrary.com/onlineopen#OnlineOpen_ Terms The Clinical Respiratory Journal ORIGINAL ARTICLE 53 The Clinical Respiratory Journal (2013) • ISSN 1752-6981 © 2012 Blackwell Publishing Ltd