I am about to perform a 2-way ANCOVA but I reject the null hypothesis in Levene's Test with a p-value of 0.023. See standard deviation and sample sizes below.

enter image description here

I googled up and down and found people saying that: 1) I can still perform the ANCOVA because the smaller group ($n=32$) has the smaller variance, and 2) I should be good to go if the smallest variance is not more than 4 times smaller than the biggest variance--> something like this:

enter image description here Does somebody here know a citable source for these two claims? They would both save me from going crazy!

Thanks a lot in advance!

  • $\begingroup$ why not use nonparametric ancova. $\endgroup$ – mandata May 14 '15 at 2:12
  • $\begingroup$ That would be plan B but I am short on time and am currently using SPSS, which to my knowledge does not offer a non parametric alternative to a two-way ancova. It would be easiest to just cite a source and continue with the current calculations (which turned out to be the way I hypothesized). Can anybody help me out with a citation? $\endgroup$ – Sam May 14 '15 at 7:26

Thanks to Henrik, an avid user of this site, I found what I was looking for:

Tabachnik & Fidell (2012, p. 86): "If sample sizes are relatively equal (within a ratio of 4 to 1 or less for largest to smallest cell size), an Fmax as great as 10 is acceptable."

Tabachnik, B. & Fidell, L. (2012). Using Multivariate Statistics (6th Ed.). New York: Pearson.

Thank you all!


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