Sir John,
I believe Peter was using this most fundamental statistical formula to arrive at his conclusion:
Percentile rank = L%i-1 + i% * (Score – LRLi) / hi
= 100* [Fi-1/FN + fi/FN*(Score–{Ui-1+ (Li-Ui-1)/2)}
(Ui-Ui-1)
i=Interval in which Score falls; i%= i’s % of total;
L%i-1=Cumulative % below interval i; LRLi=halfway pt bet. i and top of next lower interval; hi=# range of i.
Fi=Cumul. count 0 to I (FN=N); fi= count of items in i; Li/Ui=Lower/upper score of i;
36
Just plug in the variables...it's quite simple.
(Just joking....I have no idea what any of that means....just messin' with ya.)
|