where λ1k, λ5k and λ10k are λ estimated from the 1 kb, 5 kb or 10 kb window centered at the peak location in the control sample, or the ChIP-Seq sample when a control sample is not available (in which case λ1k is not used). λlocal captures the influence of local biases, and is robust against occasional low tag counts at small local regions. MACS uses λlocal to calculate the p-value of each candidate peak and removes potential false positives due to local biases (that is, peaks significantly under λBG, but not under λlocal). Candidate peaks with p-values below a user-defined threshold p-value (default 10-5) are called, and the ratio between the ChIP-Seq tag count and λlocal is reported as the fold_enrichment.
