Solved – How to sequence z-score creation and log transformation in an experiment with multiple groups and conditions

In a psycholinguistic task, participants listened to and viewed stimuli, and were asked to make acceptability judgements on them:

  • 4 conditions
  • 4 groups
  • Rating scale from 1-5

I have been advised to use z scores and log transformation (for R) on the ratings scores:


  • Should the ratings be computed into Z scores before log transformation?
  • Should computation (whether z or log first) be done by group or for the whole data set?
  • Should computation (whether z or log first) be done by condition or for the whole data set?

Best Answer

I can't see any reason to log transform AFTER making z-scores; it COULD be right to log transform and then take z-scores of the logged data. I'm not as sure on the other questions, but my intuition would be to log transform everything, then take z-scores, then do the analysis. That way, a change of 1 in a variable is the same amount in every group.

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