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I'm going to do a multiple regression analysis with two continuous IVs and their interaction. I've centered the IVs and then multiplied one with another for interaction. My problem is that the interaction variable is severely kurtotic (kurtosis 7,731, standard error=0,127, z=60.87). How should I deal with this? Removal of the most extreme cases of course helps, but what would be the most recommended way to define outliers?

N=1479 with all cases, the range of centered IVs is around 50 and the range of interaction variable around 700. The two IVs are normally distributed.

Let me know if any additional info or exact numbers would help.

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  • $\begingroup$ Hi Sanna and welcome to the site! Can you explain why you think that the kurtosis of the interaction variable may be a problem? How do the residuals of your regression look? $\endgroup$
    – COOLSerdash
    Commented Jul 10, 2013 at 7:57
  • $\begingroup$ Thanks for the welcoming! The residuals are about normally and linearly distributed, but heteroscedastic. The errors of prediction increase as the size of the prediction increases. I think the kurtosis might be a problem because regression is sensitive to outliers. Is my reasoning on completely wrong tracks? $\endgroup$
    – Sanna Jaakkonen
    Commented Jul 10, 2013 at 8:27
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    $\begingroup$ First, linear regression does not assume that the independent variables or their interaction are normally distributed. The heteroscedasticity may be a problem. Here is a good post about how to deal with outliers. This post may be informative regarding the heteroscedasticity. One proposal is to use robust standard errors or to respecify the model (or transform he variables). $\endgroup$
    – COOLSerdash
    Commented Jul 10, 2013 at 8:35
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    $\begingroup$ +1. Numerous different strategies could make sense here. Broadly speaking, dropping outliers because some of the data make analysis more challenging is about the worst. Identifying a better scale for your predictors is a better strategy. $\endgroup$
    – Nick Cox
    Commented Jul 10, 2013 at 8:44
  • $\begingroup$ Thank you COOLSerdash for the links, I'll familiarize myself with them. $\endgroup$
    – Sanna Jaakkonen
    Commented Jul 10, 2013 at 8:52

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