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A comparison of self‐reported cellular telephone use with subscriber data: Agreement between the two methods and implications for risk estimation

Epidemiologic studies on adverse health effects of cellular telephone use have assessed exposure either by self‐reported use based on questionnaire data or by using data on subscriptions for a cellular telephone provided by network operators. With the latter approach, subjects are misclassified when they regularly use a cellular telephone subscribed in someone else's or in a company name or when they subscribe for a cellular telephone which they use only occasionally. Self‐reported use is hampered by recall difficulties and possible differential participation by exposure. In Denmark, we conducted a retrospective cohort study of cellular telephone subscribers (including the entire Danish population) and a case‐control study on brain tumors and cellular telephone use (with 1355 participants) and, thus, had the opportunity to compare the two exposure measures with two large‐scale data sets, using self‐reported use as a “gold standard.” Overall, there was a fair agreement (kappa value of 0.30, 95% confidence interval 0.23–0.36), with a low sensitivity (30%) and a high specificity (94%). Agreement was slightly better for controls, and low‐grade glioma cases compared to high‐grade glioma cases and meningioma cases. A comparison of odds ratios (OR) of the case‐control data set based on either self‐reported use or on subscriber data shows no major differences, giving OR of 0.7 and 0.6 for acoustic neuroma, 0.9 and 1.1 for glioma and 0.9 and 0.7 for meningioma. A discussion of the two exposure measures reveals that they both have limitations with regard to a potential underestimation of an association and there is some concern whether they are good enough to allow a detection of possibly only subtle changes in risk. These limitations can be minimized in prospective follow‐up studies. Bioelectromagnetics. © 2006 Wiley‐Liss, Inc.