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cwillden
Super User

Games-Howell Test (Tukey HSD with Welch's correction for Unequal Variances)

This add-in allows you to performs the Games-Howell test for one nominal/ordinal group variable and one continuous response.  Games-Howell is an adjustmet to the Tukey HSD procedure to adjust the error degrees of freedom to account for unequal variances.

 

Output is similar to Fit Y by X output for the Tukey HSD procedure, which includes the Tukey HSD threshold matrix, Connecting Letters Report, and the Ordered Differences Report.  Sample output using Weight vs. Position from the Football sample data set is shown below:

 

Threshold Matrix

 

ThresholdMat.PNG

 

Connecting LettersConnectingLetters.PNG

 

Ordered Differences

 

OrderedDiffs.PNG

 

If you get a lot of value from the add-in, please let me know in the comments.  If there is sufficient interest, I will work on adding support for multiple X and Y variables, By variables, Weight, etc.

Comments
cistoladp

This add-in is most helpful and valuble - thank you!

Lyanne

I am running a oneway analysis with a block and need to use Welch's Test as the variances are not equal. This Games-Howell  add-in does not seem to interact directly with outputs, is that correct?

 

I am wondering if I need to center the data around the block and then run this add-in when I am running a oneway with a block.

 

Thanks in advance.

 

Hi @Lyanne,

 

To answer your first question, no it does not use any information from the Fit Y by X report and it is not currently able to analyze blocked data.  You could normalize by the block effects, but I think you will be anti-conservative using this add-in since it will not adjust the degrees of freedom for your block effect.

aharding

I like the approach, but wonder how powerful it is (statistical power to detect differences) compared to the weighted least squares method uisng 1/variance of each group as the weight. Have you compared these approaches?

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