Accuracy of fit and scoring model performance depends on the size of the input set. AUC performance (red line) and average Chi-square accuracy of fit of 40 descriptors (green bars), using six scoring models that were based on varying sizes of the input set. Input-set sizes are indicated with a prefix 'R' and comprised 50, 250, 500, 1000, 2000, and the complete set (3,902) of metazoan miRNA hairpins. The smaller sets were compiled by randomly selecting miRNA hairpins from the complete set. This was repeated 50 times for each set. The accuracy of fit was then calculated by averaging Chi-square test statistics over all 40 descriptors and the 50 randomly selected subsets of each indicated size. Both AUC performance and Chi-square statistics show a strong dependency on Input-set size.