Ecological Regression Analysis of Environmental Benzene Exposure and Childhood Leukaemia: Sensitivity to Data Inaccuracies, Geographical Scale and Ecological Bias

Abstract

Benzene is classified as a group 1 human carcinogen by the International Agency for Research on Cancer, and it is now accepted that occupational exposure is associated with an increased risk of various leukaemias. However, occupational exposure accounts for less than 1% of all benzene exposures, the major sources being cigarette smoking and vehicle exhaust emissions. Whether such low level exposures to environmental benzene are also associated with the risk of leukaemia is currently not known. In this study, we investigate the relationship between benzene emissions arising from outdoor sources (predominantly road traffic and petrol stations) and the incidence of childhood leukaemia in Greater London. An ecological design was used because of the rarity of the disease, the difficulty of obtaining individual level measurements of benzene exposure and the availability of data. However, some methodological difficulties were encountered, including problems of case registration errors, the choice of geographical areas for analysis, exposure measurement errors and ecological bias. We use a Bayesian hierarchical modelling framework to address these issues, and we investigate the sensitivity of our inference to various modelling assumptions.

Geographical epidemiology of prostate cancer in Great Britain

“…The "false-negative" rate will depend on the amount and spatial pattern of the true variation in risk across the study region and on the sparseness of the data (i.e., disease incidence and population at risk). Empirical evidence from previous studies suggests that the Bayesian mapping methods used here are capable of revealing clear patterns of spatial variation in risk for other relatively rare cancers such as childhood leukaemia 22,23 and larynx cancer. 24 The latter 2 studies were based on ward-level expected counts that were even sparser than the present data on prostate cancer.…”

Childhood leukaemia and non-Hodgkin's lymphoma in relation to proximity to railways

“…Harrison et al (1999) found a nonsignificant excess of leukaemia among children living within 100 m of a main road or petrol station. Best et al (2001), using different methods from ours and a range of models, found a consistent positive association between risk of childhood leukaemia and atmospheric benzene levels in Greater London in the years 1985 -1996, the areas with highest risk being clustered in Inner London. This is consistent with our findings over a different time period (1968 -1983).…”

Bayesian statistics in medicine: a 25 year review

“…Another meeting on disease clusters and ecological studies included various Bayesian developments [264][265][266]. A read paper showed a very detailed examination of projections of the AIDS epidemic [267], and another used hierarchical modelling to combine evidence on air pollution and daily mortality in the 20 largest U.S. cities [268].…”