Figure 2
![Figure 2](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1755-8794-5-43/MediaObjects/12920_2011_Article_327_Fig2_HTML.jpg)
The distribution of Pearson’s correlation coefficient (PCC) of drug-CCRG pairs. The x-axis represents PCC, the y-axis represents the frequency of a certain PCC. The value 80.6% indicates that drug-CCRG pairs whose PCC range from −0.3 to 0.3 accounts for 80.6% of all drug-CCRG pairs; 91.9% indicates that drug-CCRG pairs whose PCC range from −0.5 to 0.5 accounts for 91.9% of all drug-CCRG pairs.