Week 8

Question 1

What does ANCOVA stand for?

Answer 1

Analysis of Covariance

Question 2

What is the main purpose of ANCOVA?

Answer 2

To combine the capabilities of linear regression and ANOVA by including covariates

Question 3

What type of variables does ANCOVA include within ANOVA?

Answer 3

One or more continuous variables (covariates)

Question 4

What are the two main purposes of including covariates in ANOVA?

Answer 4

• Reducing within group ‘error’ variance
• Controlling for the influence of covariates on the DV

Question 5

In the puppy therapy example, what was the dependent variable (DV)?

Answer 5

Happiness, measured on a 10-point scale

Question 6

What are covariates?

Answer 6

Variables included in the model to adjust for their influence on the DV

Question 7

What is error variance?

Answer 7

Variance in the DV that the experiment cannot explain

Question 8

What method can be used to control for covariation?

Answer 8

• Random allocation of participants
• Matching participants
• ANCOVA

Question 9

What is one key assumption of ANCOVA regarding the covariate and DV relationship?

Answer 9

The relationship must be linear at each level of the IV

Question 10

What is meant by homogeneity of regression slopes?

Answer 10

The linear relationship between the covariate and the DV should be the same across different IV conditions

Question 11

What does it mean if the homogeneity of regression slopes assumption is violated?

Answer 11

ANCOVA should not be used to report a single overall effect of the IV on the DV

Question 12

What is the third assumption of ANCOVA regarding covariates?

Answer 12

The covariate should be independent of the experimental treatments (IV)

Question 13

What is the ideal situation for the covariate in ANCOVA?

Answer 13

The covariate shares its variance only with some of the DV’s unexplained variance

Question 14

How can you check for the independence of the covariate and experimental treatment?

Answer 14

Run an ANOVA using the covariate as the DV and the IV to check for significant differences

Question 15

What should you do if the independence of covariate and IV assumption is irrelevant?

Answer 15

Retain both covariate and IV in the model, referring to the IV as a ‘categorical predictor variable’

Question 16

What types of relationships should covariates have with the DV in ANCOVA?

Answer 16

Continuous relationships

Question 17

What statistical software is mentioned for conducting ANCOVA?

Answer 17

SPSS

Question 18

What is the significance of the effect size in ANCOVA?

Answer 18

It indicates the strength of the relationship between the IV and the DV after controlling for covariates

Question 19

Fill in the blank: ANCOVA is a special case of _______.

Answer 19

General Linear Model (GLM)

Question 20

True or False: ANCOVA can include categorical variables as covariates.

Answer 20

False

Question 21

What is an example of a covariate that may influence happiness in the puppy therapy study?

Answer 21

Individual differences in love of dogs, depression

Question 22

What should be checked for during the assumption checks in ANCOVA?

Answer 22

• Outliers
• Normality
• Homogeneity of variance
• Linear relationship between covariate and DV
• Independence of covariate and IV
• Homogeneity of regression slopes

Question 23

What statistical method is used to check for linear relationships between covariate and DV?

Answer 23

Drawing scatterplots

Question 24

What is the purpose of post-hoc comparisons in ANCOVA?

Answer 24

To determine specific group differences after finding a significant effect

Question 25

What can you do if the interaction between IV and COV is significant?

Answer 25

Run the full model with the interaction and report results in detail, but do not call it ANCOVA

Question 26

What does ANCOVA stand for?

Answer 26

Analysis of Covariance ## Footnote ANCOVA is used to compare one or more means while controlling for the effects of other variables.

Question 27

What is the main effect of the independent variable (IV) in the ANCOVA analysis discussed?

Answer 27

There was a significant effect of drink (coffee group) with age controlled for.

Question 28

What needs to be removed from the model when conducting an ANCOVA?

Answer 28

IV * COV interaction.

Question 29

What is the effect size denoted by in ANCOVA output?

Answer 29

η²p (partial eta squared).

Question 30

What was the significant effect of caffeine on reaction time in the ANCOVA results?

Answer 30

F (2, 26) = 22.15, p < .001, η²p = .63.

Question 31

What was the significant effect of age on participants' reaction time?

Answer 31

F (1, 26) = 28.82, p < .001, η²p = .53.

Question 32

What are post hoc comparisons used for in ANCOVA?

Answer 32

To analyze differences between groups when there are no priori predictions.

Question 33

What adjustment was used in the post hoc comparisons?

Answer 33

Sidak adjustment.

Question 34

Fill in the blank: ANCOVA allows you to examine differences across conditions while controlling for the effects of a _______.

Answer 34

covariate (continuous variable).

Question 35

What was the outcome of the post hoc comparison between the coffee group and the decaf group?

Answer 35

Participants in the coffee group reacted faster than the decaf group (p = .012).

Question 36

What is the effect of the decaf group compared to the control group according to post hoc comparisons?

Answer 36

The decaf group also reacted faster than the control group (p = .005).

Question 37

What should be checked before conducting an ANCOVA?

Answer 37

Assumptions about the covariate and its relationships with the rest of the data set.

Question 38

How does adding a covariate in SPSS compare to running an ANOVA?

Answer 38

It largely follows the same pattern, with additional assumptions to check.

Question 39

What is the recommended reading for ANCOVA analysis?

Answer 39

Field, A. (2024). Discovering Statistics Using SPSS (6th Ed) and Howell, D.C. (2012). Statistical Methods for Psychology (8th Ed).

Question 40

True or False: All groups were significantly different from each other once age was controlled for.

Answer 40

True.