A study of residential radon in Sweden using multi-level analysis

A Swedish radon data set, consisting of more than 8,000 measurements of residential radon levels in about 50% of the Swedish municipalities, was analyzed using a multi-level approach. The results were compared with those of a single-level analysis. We found that there was a significant variability between municipalities. The point estimates of the population mean radon levels were similar (geometric mean 60 Bq m-3 and arithmetic mean 106 Bq m-3). The analysis shows the advantages of multi-level modeling compared with a single-level ordinary least squares (OLS) model. A single-level model results in too optimistic standard errors, about 25% of those of the multi-level model, which can lead to erroneous conclusions. In a multi-level model including house type as a fixed effect (single-family house, row house, or apartment in multi-family house), the estimates of the fixed effect of house type were similar for the single-level and the multi-level models.