Table 2.

Characteristics of the study population of 13 284 subjects from northern Europe.

	Men	Women
Subjects (%)	6 253 (47.1)	7 031 (52.9)
Age the year 2000, mean (SD)	41.1 (7.2)	40.8 (7.3)
Never-smokers (%)	2 844 (45.5)	3 194 (45.4)
Ever-smokers (%)	3 263 (52.2)	3 670 (52.2)
Unknown smoking habits (%)	146 (2.3)	167 (2.4)
Not exposed (%)	2 241 (35.9)	3 372 (48.0)
Exposed (%)	3 721 (59.5)	3 257 (46.3)
Uncertain exposure (%)	291 (4.7)a	402 (5.7)b
Asthma incidence/1000 p-years	1.3	2.4

^aThere were additional 449 men, who had at least one employment with uncertain exposure.

^bThere were additional 337 women, who had at least one employment with uncertain exposure.