Curses-winner's and otherwise-in genetic epidemiology

The estimated effect of a marker allele front the initial study reporting the mnarker-allele association is often exaggerated relative to the estimated effect in follow-up Studies (the winner's Curse phenomenon). This is a particular concern for genome-wide association Studies, where markers typically must pass very stringent significance thresholds to be selected for replication. A related problem is the overestimation of the predictive predictive accuracy that occurs when the same data set is used to Select a multilocus risk model from a wide range of possible models and then estimate the accuracy of the final model (over-fitting). Even in the absence of these quantitative biases, researchers can over-state the qualitative importance of their findings-for example, by focusing oil relative risks ill a context where sensitivity and specificity may be more appropriate measures. Epidemiologists need to be aware of these potential problems: as authors, to avoid or minimize them, and as readers, to detect them.