Two Way ANOVA In SPSS
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Transcript

  • 1. Two-Way ANOVA in SPSS
    • Plan your analysis ahead of time
    • Select the same dependent variable
      • Select two factors
      • Each factor is a nominal (grouping) variable
      • If both factors have many levels (values), your analysis will be complex
    • SPSS will generate a lot of output.
    • Knowing which parts to use is important
  • 2. Set options to show Variable Names in Alphabetical Order Edit -> Options
  • 3. Use a boxplot to preview data Dependent variable Factor A Factor B
  • 4. Edited boxplot. Background changed to white. Text changed to white on outliers (doesn’t show) Notice that the labels for the variable names cut off in mid-sentence. If you edit the labels in Variable View, you can generate useful labels.
  • 5. Factorial ANOVA Analyze ->General Linear Model->Univariate
  • 6. Several steps to prepare: First: choose the variables DEPENDENT FACTOR A FACTOR B Notice that the buttons for options are vertically arranged along the side. Second, choose Options
  • 7. In the Options box …
    • Request Means for Factors
    • Request Means for Interaction
    • Request descriptive statistics
    • Request estimates of effect size (This will generate an estimate of η 2 )
    • Click CONTINUE
    • In main box, Click PLOTS
  • 8. Get a Plot of the Means of Groups
    • Put Factor with the fewest categories into the box titled “Separate Lines”
    • Put other Factor into “Horizontal Axis”
    • Click on ADD to move variable names into the Plots listing box.
    • Click CONTINUE to return to main dialogue box.
    • Click POST HOC
  • 9. Choose Post-Hoc Tests
    • Post-hoc tests are only needed if a Factor has a significant effect. You can request them now and decide later whether to use them.
    • Post-hoc tests are only needed if a factor has a significant effect AND if it has 3 or more groups
    • In this data, pricegas has 3 levels. Move pricegas to “Post hoc tests for”
    • Choose Scheff é test because groups are not equal size.
    • Note that Bonferroni (conservative) is also available.
    • Click CONTINUE for main dialogue box
  • 10. Click OK in the lower left corner
  • 11. Means of all groups Total = row or column means
  • 12. Hypothesis Test Results Factor A Factor B Interaction p -value η 2
  • 13. Post-hoc Tests All groups of pricegas differ from each other significantly
  • 14. Means Plot, Edited
    • Background made white
    • Title on horizontal axis edited for clarity
    • Chart title deleted (APA format has Figure title below the chart)
    • Legend moved inside the box for clarity
  • 15. Write-up
    • Sandwich format
    • Report three hypothesis tests with F and p- value for each:
      • Factor A
      • Factor B
      • Interaction
    • For any significant element, report means and effect size
    • For any significant element with 3 or more groups, report post-hoc tests
    • Close with a summary statement
    • Refer to boxplot or means plot as Figure 3 (or whichever number) in the write-up.