Characteristics of all study participants, cases and those with low and high levels of radon at the residences.

aEver employed in the chemical industry for at least 1 year.bTime-weighted average radon.cFor the period 1 January 1971, to censoring date with inclusion of a 10-year latency period relevant for brain tumour.dTime-weighted average NOx, we focused on the concentration of NOx as an indicator for particular matter (PM) from traffic because NOx correlates strongly with ultrafine particles in Danish streets [35].eCut-off based on the 75th percentile for time-weighted average radon concentrations.*Including 11 cases of benign tumours.