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. Author manuscript; available in PMC: 2015 Nov 1.
Published in final edited form as: Genet Epidemiol. 2014 Aug 28;38(7):610–621. doi: 10.1002/gepi.21833

Table 1. Examples of 3 pairs of SNPs in 10 individuals (P1, …, P10) that illustrate theability of the maximum relationship Rij, and maximum CCCij, i e {A,a}, j e {B, b}, to capture more meaningful and robust SNP correlations compared to PCC and r2.

Genotype of 10 individuals
|PCC| r2 max Rij max
CCCij
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10
SNP 1 Aa AA AA AA AA AA AA AA AA AA 0.1 0.0 0.9 0.5
SNP 2 bb Bb bb bb bb bb bb bb bb bb

SNP 3 Aa Aa AA AA AA AA AA AA AA AA 0.7 0.5 0.9 0.6
SNP 4 bb Bb bb bb bb bb bb bb bb bb

SNP 5 AA AA AA AA AA aa Aa AA aa aa 0.3 0.0 0.5 0.7
SNP 6 bb bb bb bb bb Bb BB Bb BB bb

Note: For the first two pairs of SNPs, P3-P10 are perfectly matched with ‘AA’|‘bb’genotypes. The only difference between the two examples is that for individual P2, SNP 1 is ‘AA’ and SNP 3 is ‘Aa’. While the PCC and r2 values are highly sensitive to this small difference, CCC exhibits little sensitivity. In the third example, SNPs 5 and 6 are perfectly matched for P1-P5 in half of the individuals and uncorrelated in individuals P6-P10. PCC and r2 were overwhelmed by the lack of correlation in P6-P10 and returned low values. In contrast, CCC looked over the heterogeneity and correctly captured a high correlation value CCCAb for the ‘Ab’ relationship in P1-P5. Note that the CCC value for ‘Ab’ is higher for this example than it is for the first two pairs of SNPs, despite the fact that had more ‘AA’|‘bb’ individuals. This is because CCC adjusts for chance pairing due to varying allelic frequencies. In the second pair, the allele frequency is 0.90 for ‘A’ of SNP 3 and 0.95 for ‘b’ of SNP 4, which gives an expected frequency of 0.73 (0.90*0.90*0.95*0.95) for ‘AA’|‘bb’ just by chance paring. Since the observed frequency of ‘AA’|‘bb’ of 0.8 is only slighter greater than expected by chance, the CCCAb value is lower. However, in the third pair, where the expected frequency for ‘AA’|‘bb’ is 0.21 and the observed frequency is 0.50, the CCC gives a high CCCAb value owing to the excess of ‘AA’|‘bb’ pairing than expected by chance.Thus, CCC is able to capture meaningful correlations more accurately than PCC or r2.