Incidence rate ratios (95% CI) for primary brain tumour risk associated with the residential radon concentrations.

aFrom 1 January 1971 until censoring, with inclusion of a 10 year latency period. The cut-off points between exposure groups were the 25th, 50th and 75th percentiles for all participants.
bAnalyses based on 51,674 cohort members and 121 brain tumours.
cAdjusted for age by using it as the underlying time scale in the Cox model and sex.
dAdjusted for consumption of fruit and vegetables, employment in the chemical industry for at least one year and traffic (time-weighted average NOx exposure between 1971 and the censoring date).
eAdjusted for employment status, schooling and marital status. Due to exclusion of cohort members with missing value in any covariate, the number of persons is identical in the crude and the adjusted analyses.