Selection bias from differential residential mobility as an explanation for associations of wire codes with childhood cancer.

Several studies of childhood cancer, especially leukemia, in residential areas have reported an association with wire configuration codes. These codes were suggested to be surrogates of electromagnetic field exposure. However, the selection criteria used in several of the studies caused the case and control populations to be non-comparable, especially with respect to residential mobility. Specifically, controls were required to be residentially stable but cases were not. Thus, an artificial association between residential mobility and cancer was created by the subject selection procedure. The present study of 5721 residences in Columbus, Ohio was conducted to learn if bias due to differences in residential mobility, rather than electromagnetic fields, could explain the reported association between wire configuration codes and childhood cancer. It was found that the proportion of homes classified as "high" wire code in the non-stable population was 31% greater than the corresponding proportion in the stable population. This finding shows that high wire codes are associated with homes in which the residents are mobile and low wire codes are associated with homes occupied by stable residents. Thus, as a consequence of this association between residential mobility and high wire codes, studies that created an artificial association between residential mobility and childhood cancer will also produce a false association between high wire codes and cancer.