The context of a study influences the reporting of symptoms

Abstract

To study whether different information on a study may influence the reporting of symptoms suspected to be related to poor indoor climate at the workplace or at home. A questionnaire was mailed to a random sample (n=4,000) of the general population in Denmark. The participants were randomly allocated to two study groups, each group receiving a slightly different information letter. There were 2,710 subjects (67.8%) who completed the questionnaire, and 2,164 subjects, who were in employment, were included in the study. All subjects were informed that the purpose of the study was to assess the prevalence of non-specific symptoms related to the indoor climate at work and in dwellings. However, in the letter to one study group it was stated that knowledge was especially lacking about health effects related to the indoor climate at work (n=1,468). To the other study group the words at work were replaced with at home (n=696). The questionnaires were similar for each study group. The prevalence rates of symptoms were similar, but reporting of work-relatedness and home-relatedness differed considerably between the two study groups. If the information letter focused slightly more on the workplace than the home, the subjects were more likely to report that their symptoms were work-related (significant unadjusted odds ratios (ORs) between 1.8 and 5.5). We found that adjusting the results for several confounders mainly led to higher estimates of ORs. Likewise, the subjects reported more home-related symptoms if focus was on the environment at home (significant unadjusted ORs between 5.7 and 20.6). The information about a study may play an important role in the reporting of symptoms.