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I wonder if it is allowed to log a variable which is already logged (transformed). When I do this, the skewness of my model goes to 0.05 which is quite good. Let me know! Thanks in advance :)

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    $\begingroup$ Sure. Everything is 'allowed' as long as you aren't breaking math. But does it actually make sense in the context of your problem? That's not something we could answer with the info provided. $\endgroup$ – Dason Dec 18 '20 at 16:41
  • $\begingroup$ Hi Dason, thank you for your reaction! The context is as following: Your client has commissioned you to conduct a survey study on the determinants of “consumer preferences” (Y-variable) for a new health service. The client wants to know the (potential) indirect effect of consumer “values” (X-variable) on these preferences via the mediator “confidence” in one’s own health (M-variable): a * b. I have 2 continuous variables, V16 (age) and V17 (mood) and they are already transformed, says the assignment. However transforming them again leads to a perfect skewness... $\endgroup$ – Mmij Dec 18 '20 at 16:54
  • $\begingroup$ @Dason, am I still allowed to log here? :) $\endgroup$ – Mmij Dec 18 '20 at 17:19
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    $\begingroup$ Can you edit your question to include the context you gave in a comment? $\endgroup$ – Ben Bolker Dec 18 '20 at 18:54
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    $\begingroup$ Is the already logged variable strictly positive? Why do you consider that a variable having small skewness is "good"? $\endgroup$ – Chris Haug Dec 18 '20 at 18:57
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Transforming the predictor variables (independent variables) to achieve a particular distribution does not make sense. We don't need particular distributions of the predictors to do regression. When we make a normality assumption, it is about the error term, not the predictors.

There might be cases where theory says that a transformed predictor variable makes more sense. There might be cases where you determine that a transformed variable results in a model with stronger performance.

But transforming the variable just because you want something that isn't skewed? I'll pass.

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