We propose a formal method to declare that findings from a primary study have been replicated in a follow-up study. Our proposal is appropriate for primary studies that involve large-scale searches for rare true positives (i.e., needles in a haystack). Our proposal assigns an r value to each finding; this is the lowest false discovery rate at which the finding can be called replicated. Examples are given and software is available.
Keywords: false discovery rate; genome-wide association studies; metaanalysis; multiple comparisons; r value.