Bias due to selection of rare variants using frequency in controls

392 volume 43 | number 5 | mAy 2011 | nature genetics investigators should be encouraged to report not only those variants that have a frequency below a pre-defined threshold in the controls but to also report those which reach the same threshold in the cases and calculate a significance level from an unbiased set of variants or, more desirably, from a permutation procedure that correctly accounts for the bias.