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         33
    47         40
    48         41
    49         83
    50         114
    51         124
    52         82
    53         89
    54         99
    55         82
    56         72
    57         80
    58         101
    59         73
    60         74
    61         81
    62         64
    63         70
    64         61

What does above data means is-

14 calls came back in 45 milliseconds
33 calls came back in 46 milliseconds
40 calls came back in 47 milliseconds
etc etc

Now I am supposed to find out 95% percentile from the above data. Meaning 95% of time, calls came back in this milliseconds.

Can anyone tell me how to do this in Excel Sheet? Thanks for the help

I am using Excel 2010. I have copied both the columns in my Excel Sheet as it is to calculate the percentage.

Update:-

With the below list, I am getting 95 percentile as 66. So that means 95% of time, calls came back in 66 milliseconds which is not right I guess. It looks to me 95% of time, calls came back in ~4ms.

Milliseconds    Number of calls
    0           11
    1           259
    2           504
    3           293
    4           38
    5           15
    6           1
    7           4
    8           1
    9           1
    10          1
    11          2
    23          1
    30          1
    39          1
    147         1

I am using this formula-

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

Answer 1

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 2

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.

Answer 3

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?