On Wed, Mar 22, 2023 at 10:46:13AM -0500, Alan Mead wrote: > When I was a young analyst, someone asked if the percentiles I'd provided > were calculated the "right way" or the "wrong way." Using the cumulative > percents is the "wrong way" (obviously, for some values of "wrong"). > > The "right way" (for some values of "right" or "correct") calculates the > percentile of the midpoint of the score category and will never be exactly 0 > nor exactly 100.
In PSPP you can choose any of 5 different ways to calculate percentiles, depending on which you considere "correct". See section 15.3 of the manual. I think you will see a difference only when the data set is very small or when there are a large number of tied scores. J'
