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Why z-scores? Transforming scores in order to make comparisons, - PowerPoint PPT Presentation

Why z-scores? Transforming scores in order to make comparisons, especially when using different scales Gives information about the relative standing of a score in relation to the characteristics of the sample or population Location


  1. Why z-scores? • Transforming scores in order to make comparisons, especially when using different scales • Gives information about the relative standing of a score in relation to the characteristics of the sample or population – Location relative to mean – Relative frequency and percentile

  2. What does it tell us? • z-score describes the location of the raw score in terms of distance from the mean, measured in standard deviations • Gives us information about the location of that score relative to the “average” deviation of all scores

  3. Z-score Distribution • Mean of zero ◦ Zero distance from the mean • Standard deviation of 1 • Standard deviation of 1 • Z-score distribution always has same shape as raw score. If distribution was positively skewed to begin with, z scores made from such a distribution would be positively skewed.

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