t test for matched samples

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t test for matched samples Matched
Samples Samples that have subjects chosen
based on shared characteristics.
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Typical matching characteristics - Gender -
Socioeconomic status (SES) - Age - IQ
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Matching subjects reduces variability that is
caused by the matching variable.
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D difference between scores of matched
subjects.
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( sum of the
differences) ( of
matched pairs, or
of difference scores)
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standard error of the
differences

Standard deviation of the difference scores
of difference scores or of pairs of scores
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Standard deviation of the differences


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Steps for a t test for matched samples 1) find
differences between matched pairs
Sample One Sample Two Sub. 1 25
22 Sub. 2 45
40 Sub. 3 30
31 Sub. 4 15 11
Sub. 5 28 22
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1) find differences between matched pairs
Sample One Sample Two D Sub. 1
25 22
3 Sub. 2 45 40
5 Sub. 3 30
31 - 1 Sub. 4 15
11 4 Sub. 5
28 22
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? D 17
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2) find average difference

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3) find standard deviation of the differences
D D2 3
9 5 25 - 1
1 4 16 6
36 ? D2 87
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4) computed standard error of the
differences
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5) compute and evaluate t
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Computed t 2.833 df n - 1 or
4 Critical value 2.776