Either that ^^^ or if you have a large sample over a pool of sponsors
https://en.wikipedia.org/wiki/Deviat...te_deviat ion
Try statistical deviation.
However, you would need a large pool of overall data for an industry -- that is known true data.
If you ask every sponsor what their rebill rate is they would just fabricate a number -- unreliable data.
Last rebill rate I recall quoted by a neutral source was years ago and it was 1.7 -- he was making the case for PPS -- so it may have been biased.