Wk 10 - Moderation with ANOVA

Question 1

What is ANOVA used for? (x1)

Answer 1

Analysing difference in means

Question 2

What kind of variables are used in ANOVA? (x2, x2)

Answer 2

Categorical IVs
*Measured or manipulated
Continuous DV
*(use logistic regression instead for categorical)

Question 3

Explain the key concept in ANOVA

Answer 3

Partitioning variance into:

* Accounted for by known factors
* And not

Question 4

How is variance partitioned in ANOVA? (x2, x2)

Answer 4

Known factors = ‘systematic variance’
*Between-groups
Unknown factors = random/unmeasured/error variance
*Within-groups

Question 5

What does between-groups variance describe in ANOVA? (x1)

Answer 5

Differences between Group Means and Grand Mean

Question 6

What does within-groups variance describe in ANOVA? (x1)

Answer 6

Differences between individual scores and Group Means

Question 7

What does the F ratio tell us in ANOVA? (x1)

Answer 7

Whether systematic variance is greater than error variance

Question 8

What do omnibus tests tell us in 2-way ANOVA? (x3)

Answer 8

Whether IVs affect DVs:
Main effect of single IVs in isolation
Interaction effects - combined multiple factors

Question 9

What don’t omnibus tests tell us in 2-way ANOVA? (x1)

Answer 9

Which means/conditions differ from one another

Question 10

How do we assess main effects in 2-way ANOVA? (x2)

Answer 10

Compare marginal means:

*Means of each level of 1 factor, ignoring the levels of the other

Question 11

How do we assess presence of an interaction effect in 2-way ANOVA? (x2)

Answer 11

Evaluate effect of 1 factor at each level of another

*Is change in scores the same (stable) across the different levels?

Question 12

How do we follow-up significant Main Effects in 2-way ANOVA? (x1, x3)

Answer 12

If 2 levels - which mean is higher?
If 3+ levels - main effect comparisons
*Pairwise t-tests
*Linear contrasts (can group multiple conditions)

Question 13

What questions are asked by follow-up tests of significant interactions in 2-way ANOVA? (x2)

Answer 13

How does pattern of means for 1 factor change across different levels of another?
How does one factor moderate effect of another?

Question 14

What follow-up tests are needed for a significant interaction in 2-way ANOVA? (x2)

Answer 14

Simple effects

*Separate 1-way ANOVAs for effect of 1 factor at each level of the other

Question 15

What follow-ups are needed for significant simple effects in 2-way ANOVA?

Answer 15

2 levels of primary factor - compare means
3+ levels of primary factor -
simple comparisons

Question 16

When should you plot the slopes/means for ANOVA? (x1)

Why? (x1)

Answer 16

Before any analyses

Easier to grasp interactions (than matrics of means)

Question 17

What does an interaction represent in ANOVA? (x1)

Answer 17

A moderating effect of 1 variable on another

Question 18

How do you identify main effects from ANOVA graphs/plots? (x2)

Answer 18

Line factor - compare average value of lines

x-axis factor - compare average values between points at each x-value

Question 19

Are main effects required to produce an interaction in ANOVA, or vice versa? (x1)

Answer 19

No

Question 20

Describe the general 3 stages of analysis plan for 2-way ANOVA (x3, x2, x3)

Answer 20

Assess omnibus effects

* Main Effects of each factor
* Interaction Effect of the two factors

Interpret significant Main Effects
*May require follow-up simple comparisons

Interpret the Interaction, if significant

* Follow-up simple effects analysis
* Simple effects analyses may require follow-up simple comparisons!

Question 21

What considerations affect the follow-up tests conducted in 2-way ANOVA?

Answer 21

How were factors manipulated?

* Both factors manipulated between participants?
* Both factors manipulated within?
* 1 factor manipulated between, 1 within?

Question 22

Describe how Ps are allocated in a 2-way between-Ps ANOVA (x2)

Answer 22

Random allocation to 1 level of 1 factor

*Each cell summarises data from different individuals

Question 23

What simple effects test do we use to follow up interactions in 2-way between Ps ANOVA? (x1, plus explain x3)

Answer 23

Series of 1-way ANOVAs for each level of primary factor

* But don't split data file into levels of the factor
* Because assume MSerror/random variance is equal across all cells
* And doesn't need recalculating for single factor

Question 24

Describe how Ps are allocated in a 2-way within-Ps ANOVA (x2)

Answer 24

All Ps complete all levels of all factors

*Cells summarise data from same Ps

Question 25

What assumption is important in 2-way within-Ps ANOVA? (x1, plus describe x3)

Answer 25

Sphericity:
Variances of levels within a factor are equal
Covariances between pairs of levels within a factor are equal
Violation of this assumption increases Type I error rate (False Alarm)

Question 26

How is the assumption of spericity evaluated for 2-way within-Ps ANOVA? (x1)
Which is interpreted such that…(x2)

And it is best to…(x1)
Because… (x1)

Answer 26

Mauchley’s Test (a chi-square)

Significance indicates violation
And need for correction to df to power down the test

Apply Greenhouse-Geisser correction universally

Mauchley’s is prone to Type 2 (misses)

Question 27

What follow-ups are used in 2-way within-Ps ANOVA?

Answer 27

Main effects - same as between-Ps (pairwise comparisons/linear contrasts)
Interactions - 1-way ANOVAs using MSerror only for primary factor in question

Question 28

How are Ps allocated for 2-way mixed factor ANOVA?

Answer 28

One factor, Ps complete all levels

Other factor, allocation to 1 level

Question 29

How are main effects followed up in 2-way mixed factor ANOVA? x2)

Answer 29

Depending on whether the factor is between- or within-Ps,

Follow steps as for an entirely between- or within-

Question 30

How are interactions followed up in 2-way mixed factor ANOVA? (x2)

Answer 30

Simple effects comprised of between- or within-Ps ANOVAs

depending of which is the primary factor