Week 5

Question 1

What are two benefits of using repeated measures?

Answer 1

1. Economy of subject numbers

2. Each subject acts as their own control

Question 2

In a repeated measures design, each subject acts as their own control. What does this in turn do?

Answer 2

Reduces the error variance, making the test more sensitive.

ie., a smaller difference between means will be sufficient to produce a significant F ratio.

Question 3

What are some disadvantages of repeated measure design

Answer 3

• order effects (due to learning or fatigue)

- differential carry over effects

Question 4

How can we compensate for order effects in repeated measure designs?

Answer 4

We can counterbalance

Question 5

What is counterbalancing? Give an example?

Answer 5

(A1, control) –> (A2, experimental)

and

(A2, experimental) —> (A1, control)

These two results will not be the same and can cause differential carry over effects.

Question 6

What are differential carryover effects?

Answer 6

Occur when counterbalancing does not balance out order effects. One particular ordering, either treatment than control or the control then the treatment, creates a reaction to the DV for that ordering only.

Question 7

what is an additional assumption in a within subjects design?

Answer 7

sphericity.

Question 8

What is sphericity?

Answer 8

compound symmetry of the covariance matrix. In other words, homogeneity of variance within treatments, and homogeneity among treatments (variances of the differences between treatments).

Question 9

When is the assumption of sphericity always met?

Answer 9

Always met when there are only 2 levels of within subjects IV (so long as you have homogeneity of variance)

Question 10

When is the assumption of sphericity usually violated?

Answer 10

Usually violated when there are more than two levels.

Question 11

What happens if the data doesn’t meet the assumption f sphericity?

Answer 11

The ANOVA becomes more generous at calling a result statistically significant.

Question 12

Are there tests to check the assumption of sphericity?

Answer 12

Yes but they are unreliable so we don’t really use them

Question 13

How do we correct for the “overly generous” results of a repeated measures ANOVA?

Answer 13

One way is to adjust the dof in the F ration by a correction factor (e, epsilon).

Question 14

What are two methods for changing the epsilon when the assumption of sphericity is violated in a repeated measures ANOVA?

Answer 14

1. Huynh Feldt

2. Greenhouse Geisser

Question 15

What is the specific test you can do to see whether or not you need to make an epsilon correction or not?

Answer 15

The Mauchly test

Question 16

What is a generalised eta squared and why would we use it?

Answer 16

measure of effect size

Can use in repeated measures as it takes sample into account

Question 17

Why is the difference between eta squared and partial eta squared in repeated measures?

Answer 17

eta squared reflects IV as a proportion of the variability in the entire study
partial eta squared (in the case of one variable) reflects how much variation the repeated measures variable explains after we have separated the effects of the differences between participants

Question 18

How do we calculate Cohen’s d?

Answer 18

Difference between means divided by some measure of pooled SD

Question 19

What is an issue with counterbalancing when we have multiple levels?

Answer 19

We increase the amount of orders that we need to counter balance, which almost defeats the purpose of the benefit in repeated measures, economy of number.

e.g., 4 levels = 4X3X2X1 = 24 different possible combinations.

Question 20

What is a more economical way to counterbalance?

Answer 20

using a latin square

Question 21

Rather than using ALL possible orders, latin square designs use a _____ of possible orders.

Answer 21

_____

Question 22

What are the two conditions of a latin square?

Answer 22

1. each treatment occurs equally often in each position in the treatment order
2. each treatment immediately precedes and immediately follows each treatment exactly equally often

most people just follow condition 1

Question 23

What is a technological way to follow conditions in making a latin square?

Answer 23

a latin square generator

Question 24

What type of puzzle are latin squares like?

Answer 24

sudoku

Question 25

What is one assumption you need when doing latin squares?

Answer 25

sphericity - if you don’t have this then you probably shouldn’t do a latin square

Question 26

If sphericity is violated, you need to adjust the ANOVA with an _____, otherwise, the analysis will be too liberal (generous).

Answer 26

Epsilon correction

Question 27

Counterbalancing ______ over come differential carryover effects.

Answer 27

WILL NOT

Question 28

What does a factorial design mean?

Answer 28

That there are two or more IV’s

Question 29

What are fixed factors?

Answer 29

IVs where the levels of each factors are chosen by the experimenter, if replicated, these would stay the same

Question 30

What are random factors?

Answer 30

Factors in which the levels if the IV are randomly selected from a larger population of potential levels. They would differ from one replication to the next.

Question 31

What is the “practical upshot” of having a random factor in an analysis?

Answer 31

it changes the way we calculate the ‘error term’ in the ANOVA (for each effect and interaction)