Objectives: To examine the temporal relationship and specificity between self-reports on the indoor environment at work and symptoms that are traditionally connected with the sick building syndrome (SBS). Methods: This questionnaire study used a prospective full panel design as regards self-reports on exposure and outcome. At the baseline, the sample comprised 2,164 adults selected randomly from the general population. Of these 1,402, who were still working and living in the same place, completed a second questionnaire a year later. Health measures were symptoms that are traditionally connected with the SBS, as well as some “dummy” symptoms that hardly can be causally related to the indoor environment. The associations between self-reports on the indoor environment and these symptom groups were assessed both in cross-sectional and longitudinal analyses, the latter examining the normal direction that exposure leads to symptoms as well as the reverse order: that symptoms lead to perceived exposure. Results: In cross-sectional analyses, the indoor environment factors were associated equally with SBS symptoms and with “dummy” symptoms. In longitudinal analyses, only few of the indoor environment factors predicted the development of any of the symptom groups. However, both the SBS symptoms and the “dummy” symptoms were risk factors for beginning to report exposures in the indoor environment. Conclusions: Symptoms predict future reports on exposures in the indoor environment indicating that it is difficult to determine what existed first: the outcome or the exposure. In addition, the perceived indoor environment is associated not only with the traditional SBS symptoms, but also with symptoms that cannot be physiologically linked to the indoor environment. These results suggest that there is a risk of reporting bias when assessing non-specific symptoms. Thus, many of the associations found in previous cross-sectional studies on SBS symptoms and indoor environment factors may possibly be explained by reporting bias.
