The feasibility of using a double blind experimental cross-over design to study interventions for sick building...

Methodological problems have limited scientific investigation of the causes of and solutions for sick building syndrome. The feasibility of using an experimental double blind cross-over study to resolve many of these methodological problems was assessed in a pilot study. The experimental intervention was to vary the amount of outdoor air from 10 cubic feet per minute per person (cfmpp) to 20 cfmpp or 50 cfmpp by central manipulation of the building heating, ventilation and air-conditioning (HVAC) system. Over 6 consecutive study weeks, 2 trials of rates were administered in random order. Study subjects and investigators of the study were blinded to intervention sequence. Unblinding, office environment rating and symptom occurrence were measured weekly. Of 305 eligible workers, 254 participated. Problems were encountered in delivering the lowest dose of ventilation due to building leakage. The prevalence of symptoms diminished steadily over the 6 study weeks, time trends which could be controlled by recommended design modifications. Blinding to the intervention was successfully maintained. Weekly non-response did not introduce a response bias but reduced the number of subjects available for analysis by one-third for each trial. We conclude that this design, with certain modifications, is feasible to evaluate many proposed interventions for sick building syndrome.