In each case subjects were asked when a particular symptom had started and whether it improved
over weekends or holidays. A smoking history was taken and any history of chronic bronchitis, hay fever, or asthma noted.
Each symptom was assessed as work related according to a standard definition: only those symptoms that had developed after the subject started work in the building concerned or, if previously present, had deteriorated after the subject started work in that building, and that improved over weekends or holidays, or both, were considered to be work related. The prevalences of symptoms reported here refer only to work related symptoms as defined above.