Smoking is the single most important risk factor for lung cancer (International Agency for Research on Cancer, 2004b), and the distribution of the cancer is likely to closely mimic that of smoking prevalence 15-20 years before the period reported here; that is, between 1975 and 1987. However, there is little available information on smoking prevalence for that period. Lung cancer risk was slightly higher in NI and showed the expected correlation with higher population density, higher unemployment and lower educational attainment. In NI the geographical pattern of lung cancer was similar for both sexes, and the higher risk was largely confined to Belfast, Derry and Newry. In RoI there were four areas of higher risk outside the main urban areas—in south Kildare and south Wicklow, around Mullingar in Westmeath and in south-east Limerick. The areas of higher risk for women were more concentrated along the east coast than those for men.
Radon levels may explain some of the geographical variation in risk, but as noted in a previous report (Carsin et al., 2009), there was no apparent correlation between areas of high lung cancer risk in RoI and average household radon levels. A lack of relationship between lung cancer risk and area measures of radon exposure has been a consistent finding of ecological studies (Puskin, 2003), partly because of the strong confounding effect of smoking (which is responsible for over 90% of lung cancers) and partly because individual exposures to radon are poorly correlated to area averages.
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