Mauchly's Test of Sphericity - how to handle data when data fails test?
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Hello,
I would like to do a repeated measures anova but my data does not pass the test of sphericity. I have very low p-values, one example shown below.
1×4 table
W ChiStat DF pValue
________ _______ __ __________
0.012023 88.971 35 1.3687e-06
Now, I read that I can correct this with Epsilon, also conducted that. I know that it is not recommended to use the Lower Bound estimate, but Greenhouse Geisser or Huynh Feldt.
But how exactly am I going to use the result from the epsilon correction on my repeated measures data? Do I choose either GG or HF and report the corrected p-value from the rm anova table? Or do I have to write some code to change the rm anova table?
1×4 table
Uncorrected GreenhouseGeisser HuynhFeldt LowerBound
___________ _________________ __________ __________
1 0.45526 0.55152 0.125
I am already thankful for your help!
regards
2 Comments
Scott MacKenzie
on 4 May 2021
It would help if you posted your data and any script you've used so far.
Answers (2)
Divyam
ungefär 17 timmar ago
To perform the right epsilon adjustment first check the corresponding p-values for the epsilon correction adjustments with respect to each term of your ANOVA analysis. You will find the respective p-values for the Greenhouse-Geisser, Huynh-Feldt and Lower-Bound adjustments in the columns "pValueGG", "pValueHF", and "pValueLB" respectively.
To correct the results, find the adjustment for which the null hypothesis is rejected and then perform the epsilon correction of the term by multiplying its degree of freedom by the corrected value of epsilon. Then, find the correct p-value for the F-distribution.
Here is an example,
Suppose
for the term "Variable1"
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1762049/image.png)
To perform epsilon correction on "Variable1", you have to perform the following correction in the DOF,
.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1762054/image.png)
To find the new p-values, you can use an F-distribution calculator and find the correct p-values by providing
& DOF as inputs.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1762059/image.png)
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