CHILDHOOD-CANCER OCCURRENCE IN RELATION TO POWER-LINE CONFIGURATIONS - A STUDY OF POTENTIAL SELECTION BIAS IN CASE-CONTROL STUDIES

Several case-control studies have reported positive associations betwe en childhood cancer and proximity to high current res idential power l ines as defined by the Wertheimer-Leeper code. We conducted a study to evaluate whether or not differential nonparticipation of controls as a function of socioeconomic status is likely to account for the observ ed associations. We assessed the relation of annual family income to t he Wertheimer-Leeper code in a sample of 392 households in western Was hington state, and we evaluated the magnitude of bias that could occur from differential participation of low- and high-income eligible cont rols. Very-high-current configurations were most frequently located am ong households with self-reported family income of less than $15,000 p er year, and very-low-current configurations were most frequently loca ted among those with self-reported family income of more than $45,000 per year. In a hypothetical case-control study in which: (1) it was as sumed that there is no true etiologic relation between power line conf igurations and cancer occurrence, and (2) controls with very low incom e were less likely to participate than others, observed (biased) odds ratios ranged from 1.03 to 1.24. If these results are applicable to ot her areas where case-control studies of cancer in relation to power li nes have been conducted, they suggest that relatively lower participat ion among exposed controls (as a function of very low income) is not l ikely to account for the elevated risks of 1.5- to 3-fold that have be en observed in these previous studies.