Table 1.

Numbers of asthmatics, person-years and incidence of asthma by onset age, birth cohort and sex

	No. of cases/No. at risk	Person-years	Incidence (95% C.I.)/1000 person-years
Whole sample	860/25,377	949,807	0.91 (0.85 ~ 0.97)
Onset age (years)
0-6	161/25,377	177,639	0.91 (0.78 ~ 1.06)
7-12	151/25,377	152,262	0.99 (0.85 ~ 1.16)
13-15	50/25,377	76,131	0.66 (0.50 ~ 0.87)
16-18	39/25,377	76,131	0.51 (0.37 ~ 0.70)
19-25	80/25,377	177,639	0.45 (0.36 ~ 0.56)
26-30	103/24,767	123,835	0.83 (0.69 ~ 1.01)
31-35	152/21,006	105,030	1.45 (1.23 ~ 1.70)
36-40	124/12,228	61,140	2.03 (1.70 ~ 2.42)
Birth cohort (age in years)
1978-1969 (26–35)	220/5,771	182,851	1.20 (1.05 ~ 1.37)
1968-1964 (36–40)	349/9,371	347,321	1.01 (0.91 ~ 1.12)
1963-1959 (41–45)	201/7,273	298,193	0.67 (0.59 ~ 0.77)
1958-1948 (46–56)	90/2,962	121,442	0.74 (0.60 ~ 0.91)
Sex
Male	300/10,016	387,436	0.77 (0.69 ~ 0.87)
Female	560/15,361	562,371	1.00 (0.92 ~ 1.08)