Association rules for discovery relationship between mortality among Chernobyl liquidators and radiation dose
The aim of the study is to classify causes of death of the Chernobyl emergency accident workers (liquidators) in compliance with ICD-10 using statistical links. For these purposes we used mortality data (27840 cases) on Russian liquidators entered the Chernobyl zone in 1986-1987. The data were collected for the period from 1986 over 2014, average external dose of g-radiation to a whole body is 0.110 Gy. To analyze statistical links between radiation doses and causes of death data mining algorithms free of a priori statements on probabilistic distributions of doses and diagnoses were used. Tables of contingency of death cases in two dose groups, group 0, dose <0.1 Gy, and group 1, dose ≥0.1 Gy, and two age groups, group 0, age <52 years, group 1, age ≥52 years, were used for analysis. Statistically significant positive association of radiation dose and death causes in similar age groups for disease in the Chapter C "Malignant Neoplasms" (age group 1) and the Chapter I "Diseases of the circulatory system" (age group 1). Statistically significant associations are in the blocs of categories C16 "Malignant neoplasm of stomach", C34 "Malignant neoplasm of bronchus and lung", I25 "Chronic ischaemic heart disease", all in the age group 1. The association is statistically significant for the diagnosis I25.9 "Chronic ischaemic heart disease, unspecified" in the age group 1. The positive odds ratio was found in the age group >52 years. This finding allows us to assume that the model of radiation risk is multiplicative because of the existence of positive correlation between radiation associated cancers and age, rather than additive. To determine correlation between causes of death and radiation dose more precisely, radiation risks should be assessed with account of results of radiation epidemiological studies of stochastic effects.