Undefined Mauchly's Test

Posted by Rudobeck, Emil (LLU) on Oct 06, 2016; 6:20pm
URL: http://spssx-discussion.165.s1.nabble.com/Undefined-Mauchly-s-Test-tp5733212.html

Given the paucity of information online, I was wondering if anyone knows the procedural approach to the evaluation of sphericity when Mauchly's test is undefined, which is the case when the number of repeated levels is larger than the number of subjects (insufficient df). I am not sure if sphericity can still be assumed based on the reported values of epsilon larger than 0.75, whether based on Greenhouse-Geisser or Huynh-Feldt. In one particular dataset, epsilon is less than 0.1. Presumably it can be assumed that sphericity is violated when epsilon is that low.

I am aware of using mixed models to overcome the assumptions of sphericity. My concern is with GLM in this case.

Citations would be welcome.

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