Calculate Percentile in Excel 2010

Question

This is my below list. I am trying to calculate 95% of calls came back in how many millseconds.

Milliseconds   Number of Calls
    45         14
    46               


        

Answer 1

Get the standard deviation of the time in milliseconds field, and use that to (95% ~ 2 x std) count the number of calls below ~2 standard deviations?

Answer 2

An extra column would simplify the calculations but you can calculate without if you want......

Assuming milliseconds in A2:A21 and number of calls in B2:B21 you can use this array formula

=PERCENTILE(IF(TRANSPOSE(ROW(INDIRECT("1:"&MAX(B$2:B$21))))<=B$2:B$21,A$2:A$21),0.95)

confirmed with CTRL+SHIFT+ENTER

or this non-array version

=LOOKUP(SUM(B$2:B$21)*0.95,SUBTOTAL(9,OFFSET(B$1,0,0,ROW(B$2:B$21)-ROW(B$2)+1)),A$2:A$21)

I get a result of 63 with both - change to 0.75 (75th percentile) and you get 59

Answer 3

Set up a new column which is "Number of Calls At or Below Time", and have it calculate the sum of the current row's number of calls, plus all numbers of calls in higher rows (lower times). Then, set up a column next to that called "Percentile", and calculate that by dividing "Number of Calls at or Below Time" by the total number of calls received. Whatever is the first row to show a percentile higher than 95% is the one which contains the 95th percentile.