| Chi square test of independence |
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| • | We
can eyeball differences between |
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| percentages
to determine whether they seem |
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| large
enough to be “important” |
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| • | Better: Are differences in percentages |
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| statistically
significant? |
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| • | Statistical
significance: are observed |
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| differences
significantly different from zero |
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| that
they could not occur by chance? |
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