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PSYC227_fall09_t_test_repeated_measures

PSYC227_fall09_t_test_repeated_measures - LearningObjec-ves...

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Learning Objec-ves Know the difference between independent‐measures and repeated‐measures research designs. Know the difference between a repeated‐measures and a matched‐subjects research design. Be able to perform computa-ons for the repeated‐measures t test. Be able to compute measures of effect size for the repeated‐measures t. Understand the advantages and disadvantages of the repeated measures design. t‐test for 2 Related Samples
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Related samples designs Repeated measures study : single sample of individuals is measures more than once on the same dependent variable Matched‐subjects study : each individual in one sample is matched with a subject in the other sample. (two individuals are equivalent) Measure same individuals twice Measure different individuals, but treat them as same
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The t sta-s-c for related samples What is the sample statistic? Reac-on -me measurements taken before and aLer taking an over‐the‐counter cold medica-on. Note that M D is the mean for the sample of D scores. Sample statistic
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we are interested in the mean difference for the general popula-on. Stating the Hypothesis
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The t sta-s-c for related samples
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Example Does birth order affect introversion? Are first‐borns more introverted than second‐borns? Administer an introversion “test” to siblings from families that have 2 children. Suppose that the introversion test yields interval scale data with high values reflec-ng high introversion.
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Pair First Born Second Born Difference 1 65 61 4 2 48 42 6 3 63 66 ‐3 4 52 52 0 5 61 47 14 6 53 58 ‐5 7 63 65 ‐2 8 70 62 8 9 65 64 1 10 66 69 ‐3 Example
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Example 1. State the hypothesis and select an alpha level. 2. Locate the cri-cal region Critical value df = n – 1 = 10 – 1 = 9
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Pair First Born Second Born Difference 1 65 61 4 2 48 42 6 3 63 66 ‐3 4 52 52 0 5 61 47 14 6 53 58 ‐5 7 63 65 ‐2 8 70 62 8 9 65 64 1 10 66 69 ‐3 3. Compute the test sta-s-c. variance
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Example Critical value Test statistic 4. Make a decision. Fail to reject the Null hypothesis
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Example Would like to assess whether birth order affects introversion. Are first‐borns more or less introverted than second‐borns? How about a two‐sided test? What changes?
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Does birth order affects introversion? Are first‐borns more or less introverted than second‐ borns? How about a two‐sided test? The cri-cal value for a 5% significance level:
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H 1 : μ D = 0 H 0 : μ D = 0 Related samples designs Repeated measures study : single sample of individuals is measures more than once on the same dependent variable Measure same individuals twice
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Example Does stress make asthma symptoms worse? The critical regions with α = .05 and df = 4 1. State the hypothesis and select an alpha level.
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