Fig. 1

Probability density curve of FPKM, CV, DPM, and FC-5% in 15,458 unigenes. The y-axes indicate the probability values for all 15,457 genes. The candidate reference genes (RGs) were preliminarily screened by four criteria including FPKM ≥ 10, CV ≤ 0.4, DPM ≤ 0.3, and FC-5% ≤ 4 (A–D). The 197 RGs that met various criteria were identified by Venn diagram analysis (E), and among these, 10 genes were selected as the novel candidate RGs. FPKM, gene fragments per kilobase of exon model per million mapped reads; CV, coefficient of variation; DPM, dispersion measure; FC-5%, the fold change between the top 5% highest expression levels divided by the bottom 5% within the 1217 samples