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Two-Way Between Groups ANOVA

Two-Way Between Groups ANOVA. Chapter 14. Two-Way ANOVAs. Are used to evaluate effects of more than one IV on a DV Can determine individual and combined effects of the IVs. The basic 2 WayANOVA situation. 2 or more Nominal Independent Variable with two or more levels

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Two-Way Between Groups ANOVA

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  1. Two-Way Between Groups ANOVA Chapter 14

  2. Two-Way ANOVAs • Are used to evaluate effects of more than one IV on a DV • Can determine individual and combined effects of the IVs

  3. The basic 2 WayANOVA situation • 2 or more Nominal Independent Variable with two or more levels • 1 Scale Dependent Variable • Effects of Drug and Age on recovery time • Effects of Exercise and Diet on number of friends • Effects of Toy Color and Gender on toy popularity

  4. One Way ANOVA is Limited • Previous data, hour of exercise by relationship status. If I want to look at sex differences for hours of exercise, I have to do a second one-way ANOVA, and it will not tell me if there is a connection between sex and relationship status on hours of exercise.

  5. Testing for Interactions • An interaction occurs when two IVs have an effect in combination that we do not see when looking at each IV individually • Two-Way ANOVAs include to nominal IVs and a scale DV • Factorial ANOVA uses one scale DV and at least two nominal IVs (factors) • Factor: IV in a study with more than one IV

  6. Why Use Two-Way ANOVAs • To evaluate effects of two IVs, it is more efficient to do a single study than two studies with one IV each. • Can explore interactions between variables

  7. More ANOVA Vocabulary • Cell: box depicting a unique combination of levels of IVs in a factorial design • Main effect: When one IV influences the DV

  8. Two Types of Interactions in ANOVA • Quantitative: interaction in which one IV exhibits strengthening or weakening of its effects at one or more levels of the other IV, but the direction of the effect does not change • Qualitative: interaction of two or more IVs in which one IV reverses its effect depending on the level of the other IV

  9. What if both IVs influence the DV? • This is an interaction

  10. Understanding Graphs • Main Effects: distance between lines • Quantitative

  11. Understanding Graphs • Interactions: slopes of lines • Qualitative

  12. Six Steps for Two-Way Between-Groups ANOVA • Step 1. Identify the populations, distribution, and assumptions. • Step 2. State the null and research hypotheses. • Step 3. Determine the characteristics of the comparison distribution. • Step 4. Determine critical values, or cutoffs. • Step 5. Calculate the test statistic. • Step 6. Make a decision.

  13. df Formulae for ANOVAs

  14. Determining the Cutoff Point

  15. Effect Size for Two-Way ANOVA

  16. Variations on ANOVA

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