To ensure an overall FDR < 5%, we found that every interaction must be reported by at least three independent assays. After eight screens 55% of the interactome was covered under these conditions. The coverage goal of 95% was achieved only after 21 comprehensive pairwise screens (Fig. 2c) . This overall outcome-that the number of experiments required to reach full coverage is two to three times that required to reach saturation-was observed over a range of error parameters (Supplementary Table 1 ). Clearly, completing the interactome map under these conditions is impractical, as it would require testing 92 million protein pairs 21 separate times.