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Dependent t -test

Dependent t -test. Varieties of t. 1-Sample (only one kind) 2-Sample (two kinds) Independent samples – groups are unrelated Experimental vs. control groups (at random) Male vs. female participants (unrelated) Dependent samples – groups are related Same person in both groups

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Dependent t -test

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  1. Dependent t-test

  2. Varieties of t • 1-Sample (only one kind) • 2-Sample (two kinds) • Independent samples – groups are unrelated • Experimental vs. control groups (at random) • Male vs. female participants (unrelated) • Dependent samples – groups are related • Same person in both groups • Left hand vs. right hand • Pain-free vs. placebo • Groups are related somehow • Wife, husband • Cancer patient, friend

  3. Dependent t Formulas Observations come in pairs. Brother, sister, repeated measure. Dependent t is equivalent to a single sample t computed on differences. Problem solved by finding diffs between pairs Di=Xi1-Xi2. df=N(pairs)-1

  4. Dependent t Example

  5. Six Steps • 1. Alpha = .05 • 2. Null & Alt: • 3. Calc stat: • 4. Crit value: df = N-1 =2, alpha .05, 2 tails. • 5. Decision rule: • 6. Conclusion: t = 4.30 Reject if |tobt| > tcrit N.S., i.e., no difference.

  6. Faces – how attractive are they? A B Rate each face on a scale from 1 to 10 where 1 is unattractive and 10 is extremely attractive.

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