I am a biologist, and I know this is a very basic question in the psychological realm. In psychological and neuropsychological test batteries, when dealing with patients' scores, I see that the common practice is to display the t-scores and z-scores, rather than the raw score.

  • why psychologists prefer t and z values rather than a raw score?
  • how is that interpreted?
  • a t-value and z-value in comparison to WHAT?

In any other situation, a t-statistic would be the result of comparing 2 means, and the t´s would tell me how far or close I am from the mean. Is it the same in a psychological scenario? But then again, what were the comparison values to start with? More specifically, what is a good and a bad result?



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