"PthPercentile" function in Crystal Reports

I am currently using Crystal Reports to calculate 75th percentile of a data set and was asked to provide the percentile methodology/formula/algorithm being used by Crystal Reports (as there are different methods).

Others have noted reasons for differences in the percentile results between Crystal and other tools (e.g. http://www.tek-tips.com/viewthread.cfm?qid=1270864 ), so I am hoping that SAP official documentation exists for this topic that I can reference.

I have searched the SAP community Q's and A's and Crystal documentation but cannot find this information. Any direction/assistance is greatly appreciated. Thank You in advance.