Qlik Community

QlikView Documents

Documents for QlikView related information.

Announcements
QlikView Fans! We’d love to hear from you.
Share your QlikView feedback with the product team… Click here to participate in our 5-minute survey.
Rules, plus terms and conditions, can be found here.

Standard Deviation (Population vs. Sample)

Standard Deviation (Population vs. Sample)

Inspired by swuehl‌'s response here: Help with Standard deviation Full population No... | Qlik Community I thought it make sense to share a way to calculate population standard deviation as QlikView's Stdev() seems to be a sample standard deviation. The difference between the two becomes negligible as the number of data point increases, but there might be a use case to apply population standard deviation for a smaller dataset.

I start with no dimension in an Excel file

Capture.PNG

If you look at the statestic box, you will see that the standard deviation will show the sample stdev number

Capture.PNG

Also, when you use =Stdev(Data1), it will show the same number as above. In order to get population stdev, all you need to do is to multiple the standard deviation with this

=Stdev(Data1) * sqrt((Count(Data1)-1)/Count(Data1))

In other words, I am multiplying the Sample standard deviation with Sqrt((Number of Observations - 1)/Number of observations). So, for the above sample it would be Sqrt(9/10).

Capture.PNG

And the same logic can be carry forward to a table to create confidence intervals using TOTAL qualifer

Sample

=Stdev(TOTAL Data1)

Population

=Stdev(TOTAL Data1) * sqrt((Count(TOTAL Data1)-1)/Count(TOTAL Data1))

Capture.PNG

Same idea can be applied if you want to calculate Sample or Population Standard Deviation by Dimension

Capture.PNG

In the a chart, you can use these expressions

Sample

=Stdev(TOTAL <Region> Data3)

Population

=Stdev(TOTAL <Region> Data3) * sqrt((Count(TOTAL <Region> Data3)-1)/Count(TOTAL <Region> Data3))


Capture.PNG

Tags (2)
Labels (2)
Attachments
Version history
Revision #:
1 of 1
Last update:
‎01-25-2018 03:49 PM
Updated by: