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Raw Scores below
Raw scores above
(+) z-scores Z-scores
Benefits of using z-scores: Can compare standardized scores when
original units of measurement differ
Calculate percentile ranks
Look for outliers in data for a variable
Rule of thumb: + 3 standard deviation units
Rule Z-Score Formula & Example
If a variable has M = 100 and SD = 50,
the z-score for a raw score of 200 is:
200 is: X − μ 200 − 100
Interpretation: The raw score is two SDs
(2 increments of 50) above the mean.
(2 Finding Normal Probabilities
Probability is the
Probability is measured
area under the
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This document was uploaded on 02/19/2014.
- Spring '14