Effect of larger variance in covariate (or: getting closer to a normal distribution) on result of ANCOVA

#1
Hello,

I have a question about ANCOVA.

We did an experiment with 2 groups and then calculated an ANCOVA to see if the DV differed between the groups.

We included one binary and one continous covariate (PO). Both did not sig. differ between groups.

It was criticized that PO is skewed - we have more participants with a low PO score than those with a high PO score. It was suggested that we resample and specifically recruit those with a high PO score.

I got the tip to argue that such a change in covariate (e.g., getting closer to a normal distribution) would probably not bring major changes in the result, only smaller standard errors. However, the person did not know the exact reasoning for this anymore.

Can someone here perhaps give me a hint how I could justify this and/or literature tips on this? My research has been unsuccessful so far....

Thanks!
 
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