The control group was made up of children who died from causes associated with respiratory complications. The controls were pair matched to the cases in respect to gender, year of birth, and year of death after they had been selected randomly from the set of possible controls for each case.
The results were that, cancer cases had considerable higher rate of 87.3% of occurrence for those residing in urban municipalities than that of controls of 80.5%. They further revealed that, the crude odds ratios were considerably higher than 1.0 for the groups with high levels of nitrogen dioxide exposure in their residential municipality. This implies that, there was a considerable trend toward an increased risk of childhood leukemia with rising nitrogen dioxide concentrations.
The findings of this study are consistent with previous studies as reflected in the problem statement. This study offers further evidence of a relationship between exposure to traffic exhaust emissions and the risk of childhood leukemia. The findings of this study call further investigation of the role of traffic air pollution in childhood leukemia.