1. Two Way ANOVA
A way to look at the effects of two independent variables and their interactions.

2. Research Designs
The study has two independent variables, factor 1 (e.g. personality) and factor 2 (e.g. situation)
Each factor has a certain number of levels (e.g. 2 personality traits and 2 situations).
They are completely crossed to create the appropriate number of conditions (e.g. 2 traits X 2 situations = 4 cells)

3. Research Designs
Factor 1: Half the participants have personality trait A and half the participants have trait B
Factor 2: Half the participants were observed in private and half were observed in public
Dependent variable: amount of food consumed

4. Research Designs 100 140 70 85 Trait A Trait B µpublic µprivate
In public
In private
This allows us to ask three important research questions:
1. On average, is there a difference between the two situations?
H0: µpublic = µprivate
HA: µpublic ≠ µprivate
Testing the “Main Effect” of Situation

5. Research Designs 100 140 70 85 Trait A Trait B µpublic µprivate
In public
In private
µtraitA
µtraitB
This allows us to ask three important research questions:
2. On average, is there a difference between the two personality types?
H0: µtraitB = µtraitB
HA: µtraitB ≠ µtraitB
Testing the “Main Effect” of Trait

6. Research Designs 100 140 70 85 Trait A Trait B µpublic µprivate
In public
In private
µtraitA
µtraitB
This allows us to ask three important research questions:
3. Does the effect of situation depend on personality? (or vice versa)
H0: no interaction
HA: interaction
Testing the Interaction Effect

7. Bar Graphs
A main effect of situation.
No main effect of trait.

8. Bar Graphs A main effect of situation. No main effect of trait.
A main effect of trait.
No main effect of situation

9. Bar Graphs
Two main effects

10. Bar Graphs
Two main effects

11. Bar Graphs
Two main effects
No interaction

12. Bar Graphs Two Main Effects and an Interaction
“The effect of trait is more pronounced in public”

13. Bar Graphs Two Main Effects and an Interaction Same data!
“The effect of situation is more pronounced in people who have trait A2”

14. Bar Graphs
No Main Effects and an Interaction

15. Line Graphs
A main effect of situation.
No main effect of trait.

16. Line Graphs A main effect of situation. No main effect of trait.
A main effect of trait.
No main effect of situation

17. Line Graphs
Two main effects

18. Line Graphs Two Main Effects and an Interaction
“The effect of trait is more pronounced in public”

19. Line Graphs Two Main Effects and an Interaction Same data!
“The effect of situation is more pronounced in people who have trait B”

20. Line Graphs
No Main Effects and an Interaction

21. Graphing Same Data Different Ways
How you graph it influences what you see

22. Graphing Same Data Different Ways

23. Graphing Same Data Different Ways

24. Graphing Same Data Different Ways