To detect differentially expressed small RNAs in paired samples, two statistical test methods were used by CPSS. When the counts of the tag are smaller than 5, Fisher's exact test will be used for judgment. A chi-square test will be used if the counts is more than 5.Additionally, the expression of each tag was normalized based on the absolute number of mappable reads (Normalized counts=Reads per Million). The fold change was calculated based on the normalized value.
For group samples, Kolmogorov–Smirnov test is used to generate P-value. Fold change is calculated using the same method above.