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Raw Scores below
mean have
mean
() zscores
()
Raw scores above
Raw
mean have
(+) zscores Zscores
Zscores
Benefits of using zscores: Can compare standardized scores when
Can
original units of measurement differ
original
Estimate probabilities/proportions
Calculate percentile ranks
Look for outliers in data for a variable
Rule of thumb: + 3 standard deviation units
Rule ZScore Formula & Example
ZScore
If a variable has M = 100 and SD = 50,
If
the zscore for a raw score of 200 is:
zscore
200 is: X − μ 200 − 100
Z=
=
= 2.0
σ
50
Interpretation: The raw score is two SDs
Interpretation:
(2 increments of 50) above the mean.
(2 Finding Normal Probabilities
Finding
Probability is the
Probability is measured
area under the
curve! under...
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This document was uploaded on 02/19/2014.
 Spring '14

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