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:

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### Questions:

- 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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