Comments on: Standard Deviation of Counts

by: Ross

Tue, 20 May 2008 11:24:18 +0000

Hi Jelle-Jeroen,
Thanks, thats fine no worries,
Cheers
Ross

by: Jelle-Jeroen

Tue, 20 May 2008 08:43:02 +0000

Ross,

I toke the liberty to post it, If you’ve got any problems with that I will remove it.

Jelle-Jeroen

by: Jelle-Jeroen

Mon, 19 May 2008 06:33:25 +0000

Ross,

Do you mind if I write a topic on my own blog about this…..?

Jelle-Jeroen

by: Jelle-Jeroen

Sun, 18 May 2008 13:53:12 +0000

Ross,

After reading Rob’s post I toke his way of thinking and wrote an array function for all the rows.
Its a little bit long but checked out correctly….. ( I think )

{=SQRT((SUM(counts)*SUM(MMULT(values^2,TRANSPOSE(counts)))-((SUM(MMULT(values,TRANSPOSE(counts))))^2))/(SUM(counts)*(SUM(counts)-1)))}

by: ross

Wed, 14 May 2008 11:46:45 +0000

Hi Rob,
Thanks I’ll take a look at that, it looks like it makes sense. I did try to use a SP, but i got a bit stuck with zeros!
Cheers
Ross

by: Rob

Tue, 13 May 2008 17:43:18 +0000

a sumproduct and a bit of maths should do the trick (if i understand you correctly).

for the top line of results,:
=SQRT(SUMPRODUCT((values_range-mean)^2,count_range))/(n-1)) and entered as an array formula (ctrl-enter).

it wouldn’t extend simply to a multirow version but you could just have an extra column of ‘total deviations’ and then add em up, divide by n-1 and sqrt.

Rob

by: ross

Wed, 07 May 2008 13:54:36 +0000

Hi Jelle-Jeroen,
I recheck the function, you are right, it works correctly for some sets, but is incorrect for others! I’m not sure why, will have to look into it a bit more,

re Doh:
its what Homer says when re realises hes made a mistake - like i did by looping, rather than just add up the totals in the range, - i did appreciate your remarks, thanks.
http://www.arar93.dsl.pipex.com/mds975/Images/homer_simpson_doh_02.gif

by: Jelle-Jeroen

Wed, 07 May 2008 13:24:37 +0000

Ross,

What was your Standard deviation…?
Did you have 167 scores….?

I’m dutch and didn’t understand your remark: Doh!!!!
Do you appreciate my remark or didn’t you

Jelle-Jeroen

by: ross

Wed, 07 May 2008 10:32:09 +0000

Hi Jelle-Jeroen,

ReDim Scores(1 To WorksheetFunction.Sum(Counts))

Doh!!!!!

Mine semed to work for my data - i did check the results!!! maybe we have it set up diffrently?

by: Jelle-Jeroen

Mon, 05 May 2008 11:09:11 +0000

Using your function I get a Standard Deviation equal to 1.4142135623731

But if you manually calculate the Standard Deviation of the 167 scores the answer is 1.01215468673352 ( asuming this is a partial sample of the whole population)

I ajusted your code

Function SDCOUNTS(Counts As Range, Values As Range)

Dim Scores() As Double

Dim i As Integer
Dim j As Integer
Dim k As Integer

k = 1

ReDim Scores(1 To WorksheetFunction.Sum(Counts))

For i = 1 To Values.Cells.Count
For j = 1 To WorksheetFunction.Sum(Counts.Columns(i))
Scores(k) = Values.Cells(1, i).Value
k = k + 1
Next j
Next i

SDCOUNTS = WorksheetFunction.StDevP(Scores)

End Function

Cheers