Hi All,

The existing Percentile class calculates the percentile based on the quantile 
position of the array fixed as 

p * (N+1)/100 for a pth Percentile on an Array of size N. However if we were to 
add these numbers in MS Excel
to calculate the percentile it provides a different result and closely 
resembeles the formula [p*(N-1)/100]+1.
Its imperative at times to match the computations to a standard spreadsheet 
calculations or to a standard tool;
which is why i request for allowing the quantile position to be customized. 
Infact even the kth selection used 
can also be refactored as a strategy(than as a private methods) as a further 
step.

So if atleast the Percentile class were to allow the quantile position to be 
customized in the sub classes; then 
the end user may be helped in providing the formula of their choice.

The most minimal change i am proposing here is to just make the quantile 
position setting as a protected method and i have attached a possible patch in 
[MATH-1120].

Request all to opinionate on this 

thanks
venkat

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