Fig. 3

Illustration of how uncertainty in mutation frequency estimates can lead to over-estimation of the number of mutations above the frequency threshold, even if the estimated frequencies are unbiased. The red and blue shaded areas correspond to mutations for which sampling error could cause them to cross the frequency threshold (i.e. the estimated frequencies of mutations with true frequencies in the red shaded area may be below the threshold due to sampling error, while the estimated frequencies of mutations in the blue shared area may be above the threshold). Because the blue shaded area is much larger than the red area, the number of mutations that pass the threshold from left to right is likely to be much larger than the number of mutations that pass the threshold in the other direction, leading to over-estimation of the number of mutations above the threshold