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Inferences: Tests with More than Two Groups

Inferences: Tests with More than Two Groups. Objective : Understand inference tests used with more than two groups. Outline. ANOVA ANCOVA MANOVA/MANCOVA Chi-square tests (non-parametric) Regression (brief intro) HLM, SEM. Analysis of Variance (one-way).

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Inferences: Tests with More than Two Groups

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  1. Inferences: Tests with More than Two Groups Objective: Understand inference tests used with more than two groups PRE 715: Introduction to Reserach Methods in Education

  2. Outline • ANOVA • ANCOVA • MANOVA/MANCOVA • Chi-square tests (non-parametric) • Regression • (brief intro) HLM, SEM

  3. Analysis of Variance (one-way) • Purpose: make inferences about means for three or more groups on DV • “One-way” because one IV and one DV • IV = nominal or ordinal; DV = interval or ratio • Groups or levels of IV must be independent • Null is that all means on DV are the same for all groups • ANOVA uses the F-distribution

  4. Analysis of Covariance (ANCOVA) • Same as ANOVA but… • Controls for the influence of another variable on the DV • Null hypothesis is equal means across groups, after controlling for a variable.

  5. Practice Quiz Questions 1. ANOVA/ANCOVA tests use a _________ distribution while t-tests use a ___________ distribution. 2. The main difference between and ANOVA and an ANCOVA is: • ANOVA requires a DV that is nominal or ordinal, ANCOVA requires a DV that is ordinal or interval • ANOVA controls for the effects of other variables, ANCOVA does not • ANOVA can only have one DV and one IV, ANCOVA can have two or more DV’s and one IV • ANOVA cannot control for other variables while ANCOVA can.

  6. Practice Quiz Questions 1. ANOVA/ANCOVA tests use a __ F ____ distribution while t-tests use a __ t _____ distribution. 2. The main difference between and ANOVA and an ANCOVA is: • ANOVA requires a DV that is nominal or ordinal, ANCOVA requires a DV that is ordinal or interval • ANOVA controls for the effects of other variables, ANCOVA does not • ANOVA can only have one DV and one IV, ANCOVA can have two or more DV’s and one IV • ANOVA cannot control for other variables while ANCOVA can.

  7. MANOVA/MANCOVA • Uses F-distribution • Can have multiple DV’s! • DV’s interval or ratio; IV’s nominal or ordinal • Controls interval or ratio (MANCOVA) • Tests if there are mean differences for the group of DV’s as a whole

  8. Differences Learning and Negative Experiences in Youth Activities Versus Comparison Activities

  9. What would be the correct test if…? • 1 DV = Interval; 2 IV’s = Nominal • 1 DV = Ratio; 1 IV = Ratio • 4 DV’s = Interval; 4 IV’s = Ordinal • 1 DV = Nominal; 2 IV’s = Nominal

  10. What would be the correct test if…? • 1 DV = Interval; 2 IV’s = Nominal • ANOVA • 1 DV = Ratio; 1 IV = Ratio • Correlation • 4 DV’s = Interval; 4 IV’s = Ordinal • MANOVA • 1 DV = Nominal; 2 IV’s = Nominal • Chi-square

  11. Summary • Reminder: using inference tests to make population inferences from sample data Applying your knowledge of inference tests: • Understand the level of measurement • Understand exactly what is being measured! • Determine if appropriate test is appropriate • Decipher/study what the results mean • Magnitude of significant differences? • Direction of significant findings? • What is NOT significant? • Evaluate discussion section • Are author conclusions accurate given variables, tests used, and sampling method?

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