How is a runner’s Performance Index calculated?

A runner's Performance Index (PI) provides a measure of the strength of a runner's race performances over the past 12 months. 

To calculate a runner's PI, we take a runner's race results for the past 12 months and average the individual race result PIs in that period. 

Note that, as discussed in the PI calculation methodology, backyard ultras, races with fewer than 20 participants and non-standard fixed-time races (fixed-time races other than 6h, 12h, 24h, and 48h) are excluded from PI calculations and the runner PI average.