Epidemiology of Electromagnetic Fields

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Selection and Detection Bias

Maria Feychting

Introduction

In epidemiological studies of rare diseases, prospective collection of detailed exposure

information for each individual in the entire study base may be very time consuming

and expensive, because the study base must be very large to achieve sufcient statistical

power. A cohort design may therefore not be feasible, unless exposure assessment can

be made through registry-based sources independent of participating cohort members.

Therefore, a more efcient and less expensive alternative is to perform a case–control

study that identies cases that occur over a certain time period and w