to self-reported versus measured overweight status). Figure 2 illustrates that even modest misclassification can greatly decrease the power of tests for G*E interaction (and the relative decrease is greater for rare exposures). On the other hand Figure 2 also illustrates that a large study using the proxy can have greater power than a smaller study using the perfect measure, although the power gain is modest at best. Nevertheless, the modest power gain may be important when the perfect measure is prohibitively expensive or only available on a small fraction of samples, while the good measure is relatively inexpensive or already available on many samples.
