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Post Hoc Tests

Post Hoc Tests. Chapter 14 Homework: problem 1. Interpreting ANOVA. ANOVA: testing omnibus null hypothesis H 0 : m 1 = m 2 = m 3 = … = m k Accept H 0 all possible pairwise and complex H 0 are true Reject H 0 at least one is false do not know which one(s) ~. Post Hoc Tests.

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Post Hoc Tests

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  1. Post Hoc Tests Chapter 14 Homework: problem 1

  2. Interpreting ANOVA • ANOVA: testing omnibus null hypothesis • H0 : m1 = m2 = m3 = … = mk • Accept H0 • all possible pairwise and complex H0 are true • RejectH0 • at least one is false • do not know which one(s) ~

  3. Post Hoc Tests • Post hoc: after the fact • only after rejecting ANOVA H0 • Hypothesis tests • Determine which means differ from each other • or combination of means • complex hypotheses • several different types of post hoc tests ~

  4. Post Hoc Tests • Cannot use t test • must set abefore collecting and examining data • e.g., flip a coin • P(heads), before you flip? • P(heads) if you flip and peek? • ANOVA then t test is like peeking • P(Type 1 error) no longer a = .05 ~

  5. Post Hoc Test: Tukey’s HSD • HSD: honestly significant difference • Use to test pairwise H0 • only after significant ANOVA • Test statistic is Q • studentized range statistic (A.5, p480) ~

  6. Post Hoc Test: Tukey’s HSD • MSW is mean squared within groups • s2pooled • unequal n use MSW from ANOVA ~

  7. Tukey’s HSD: QCV • Table A.5, p. 480 (a = .05) • p. 481 (a = .01) • need 2 pieces of information • 1st column: dfW • (nG - k) • 1st row: k = # groups • NOTdfB = k - 1 • Find QCV same as others ~

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