Application of the case-specular method to two studies of wire codes and childhood cancers

This paper presents the results of applying the case-specular method to two earlier studies of wire codes and childhood cancers (DA Savitz er al, Am J Epidemiol 1988;128:21-38, and SJ London et al, Am J Epidemiol 1991;9:923-9 37). The method compares the wire codes of case residences with the wire co des of specular residences constructed by switching the Location of the cas e residence across the center of the street. The method was designed to dis criminate between the magnetic field hypothesis, which postulates that chil dhood cancer is affected by magnetic fields and that wire codes are a proxy for magnetic fields, and the neighborhood hypothesis, which postulates tha t childhood cancer is affected by some characteristics of the neighborhood other than magnetic fields and that wire codes are a proxy for those charac teristics. Although the results from the two applications of the method hav e limited precision, they support the results originally reported (odds rat ios of around 2 for very high current configuration residences and childhoo d cancers) and do not support suggestions that the associations are due to confounding by socioeconomic and neighborhood factors. The results leave op en the question of whether or not control selection bias could have influen ced the original associations, because there was no convincing evidence tha t the control-specular matrices were symmetric.