Two-way between-subjects ANOVA

Question 1

factorial anova

Answer 1

more than one factor

variables can interact and the effects of one. on another may differ according to te level of the other factor

Question 2

what does 2-way b-s anova allow?

Answer 2

comparisons of 2 or more groups at the same time but groups can have more than one IV

2+ IV with 2+ levels

look at the main effect of each IV alone and the main effect of the interaction

Question 3

SPSS outputs for 2-way between-subjects anova

Answer 3

• Between subjects factors (levels of factors)
• Descriptive statistics (means and IDs for the factors separately and their interaction)
• Levene’s test of between-subjects effects (‘based on mean’ row - p>.05 (non sig) shows variances within-groups aren’t significantly different from each other)
• Tests of between-subjects effects (ANOVA stats for reporting main effect/interaction) (F equation with eta square)
• Profile plots (graph of interaction where parallel lines show no significant interaction)

Question 4

equation for effect size for 2-way b-s anova (eta square)

Answer 4

sum of squares for the factor or interaction / total sum of squares

Question 5

Cohen’s guidelines for effect sizes

Answer 5

s = 0.01
m = 0.059
l = 0.138

Question 6

formally reporting anova

Answer 6

• ANOVA type, effect of factor/IV on DV
• Present means and SDs
• Mention assumptions
• Report ANOVA results giving DF, F ratio and p value
• Report effect sizes and what it means
• Report all main effects and interactions
• Report comparisons
• Interpret in words

Question 7

Interpreting factorial anova

Answer 7

• ANOVA table shows which main effects and interaction terms are significant
• main effects = follow up with (un)planned comparisons for factors wth more than 2 levels
• Interactions = follow up with simple effects (using t-tests)

Question 8

What is the Bonferroni adjustment/correction and why use it?

Answer 8

used to reduce type 1 error

p<.05/no. of comparisons you are making