Simulation result of sequence depth vs. miRNA capture. The original library has ~25.4 million single end reads. miRNAs are defined as expressed at an arbitrary cutoff of > =2 reads and clustered into five expression level groups based on the number of assigned reads. The original library is randomly sampled at 14 different depths from 0.5M to 24M. For each of the five groups from each sub-library, the number of miRNAs with > =2 reads are calculated and the ratio over the corresponding total from the original library is displayed. About 78% of expressed miRNAs can be detected at sequence depth of 12–18 million of reads.