Lecture 10- Repeated Variance

Question 1

What is systematic variance

Answer 1

Created by our manipulation

Question 2

Unsystematic variance

Answer 2

Variance created by unknown factors

Question 3

Positives of repeated measures designs

Answer 3

• Unsystematic variance is reduced
• Less participants are needed
• More sensitive to experimental effects

Question 4

Approaches to repeated measures designs and the GLM

Answer 4

• Assume sphericity (estimate it, adjust the degrees of freedom)
• Fit a different kind of model (a multilevel growth model)

Question 5

What is the assumption of sphericity

Answer 5

The differences between pairs of groups should have equal variance

Question 6

How is assumption of sphericity estimated

Answer 6

• Greenhouse-Geisser estimate, Ê

- Huynh-Feldt estimate, Ē

Question 7

What does it mean if E = 1

Answer 7

Sphericity is perfect

Question 8

What does it mean if E < 1

Answer 8

Sphericity is violated to some degree

Question 9

How do you correct the effect of sphericity

Answer 9

Multiply df by the estimates

Question 10

Given that E quantifies the deviation from the perfect sphericity we correct the df by

Answer 10

the degree to which sphericity is violated

Question 11

How does the df getting smaller affect sphericity

Answer 11

Makes it harder for the test to be significant

Question 12

If u were to forget about sphericity you would have to

Answer 12

Routinely apply the G-G correlation

Question 13

How do you specify repeated measures with afex::aov4() function

Answer 13

(Rm predictors|id variance)

Question 14

With the afex::aov_4() function how do you build in interaction plot

Answer 14

afex_plot()

Question 15

What package is lmer() from

Answer 15

lme4

Question 16

When the repeated measures model is too complex to fit, the simplest version instead

Answer 16

Treats the predictor variables as fixed

Question 17

what does j represent in the GLM

Answer 17

Different participants

Question 18

b0j represents

Answer 18

b0 + u0j

u0j= variability across different participants

Question 19

In post hoc tests how do you work out if something is significant

Answer 19

If the p value is smaller than the p critical value

Question 20

What is true about sphericity

Answer 20

• It is automatically met when a variable has only two levels
• If it is not met then it is remedied by adjusting the df by the degree to which the data are not spherical

Question 21

What is the column ges in afex::aov_4

Answer 21

• Generalised partial eta-squared

- Explains the percentage of the variance in the outcome

Question 22

What assumption of the linear model is automatically violated in repeated measures designs

Answer 22

Independence of errors