Effective coverage (λeff) is a metric that measures the spatial uniformity of sequencing reads in a sample relative to a haplotype reference panel. It is defined as a function of the fraction of polymorphic sites covered by at least one sequencing read and is calculated as λeff = −ln(1 - fcovered), where fcovered is the fraction of n sites in the imputation panel covered by sequencing reads. Effective coverage differs from nominal (mapped) coverage, which simply measures the amount of sequenced data available for analysis, and is considered to be a more useful indicator of the quality of sequencing results, as it also considers the _breadth_ of coverage, which is important for accurate genotype imputation.

You can learn more about effective coverage in our paper entitled, *Low-pass sequencing increases the power of GWAS and decreases measurement error of polygenic risk scores compared to genotyping arrays *