Residential epidemiologic case-control studies examining the relationship
between contemporary 222Rn gas concentrations and lung cancer have
been performed in Canada, China, Finland, Germany, Spain, Sweden,
the United Kingdom, and the United States. A meta-analysis of eight
studies using weighted linear regression found a summary excessive
risk of 14% at an average indoor 222Rn gas concentration of 4 pCi/L.
The excess risk at 4 pCi/L in recent studies in Germany and the United
Kingdom was in close agreement with risk estimates obtained from
the meta-analysis. The meta-analysis risk estimate was also consistent
with the risk estimate extrapolated from miner studies. Additional
residential case-control studies currently in progress in the United
States (Missouri and Iowa) and Europe incorporate improved estimates
of retrospective exposure to 222Rn progeny. In addition, the pooling
of data from published and ongoing case-control studies is currently
in progress.