| Correlation between | Correlation coefficient | p-value |
| PPI and RS1 repeats | −0.240 | 0.346 |
| PPI and RS3 repeats | −0.0192 | 0.936 |
| Age-adjusted PPI and RS1 repeats | 0.309 | 0.222 |
| Age-adjusted PPI and RS3 repeats | 0.0297 | 0.906 |