Does anyone have a code with the formulae for calculating the FAA's percentage within limits?
I can calculate the number of samples (N), standard deviation (Sn), lower quality limit (Ql), and upper quality limit (Qu). The formulae apparently uses a beta distribution. For a single-sided calculation (Ql only), I found this on an old spreadsheet:
Ncalc = N/2-1
Alow = MAX(0,0.5-0.5*Q*(N^2/(N-1))) 'I do not know what this does for me or where the internal formula came from. Why take the max value?
BetaL = MAX(0,BETADIST(Alow,Ncalc,Ncalc,0)) 'What does the 4th BETADIST argument do? I just know that it works. Why take the max value?
PWL at Ql = 100*(1-BetaL)

How would this change for calculating the PWL at the Qu?