Chapter 8: Between groups design

Question 1

Between-groups design

Answer 1

2 or more groups are formed from a pool of subjects
Groups are independent
Each group receives different experimental treatment and the scores for the groups are compared

Question 2

How to look for the effect of the IV?

Answer 2

By comparing the mean scores (DV) for each group

Question 3

Systematic variance

Answer 3

Difference in the DV between groups

Large between group variance is good

Question 4

Non-systematic variance

Answer 4

Variations in scores within groups (individual differences occurring by chance)
Large within group variance is bad

Question 5

How to determine statistical significance?

Answer 5

between group variance / within group variance

Question 6

How to keep within group variance low?

Answer 6

By ensuring that the groups are equivalent

Question 7

How can groups be equivalent? (3)

Answer 7

1) Created equally
2) Treated equally (except for IV)
3) Composed of equivalent individuals

Question 8

Randomization

Answer 8

Participants randomly assigned to groups to ensure groups are as equal as possible before treatment/intervention

Question 9

Randomization techniques (3)

Answer 9

1) Free random assignment (e.g., coin toss)
2) Matched-group
3) Randomized block

Question 10

Matched-group

Answer 10

Match subjects on pre-existing differences which may be related to differences in the DV

Question 11

Randomized block

Answer 11

Matching is extended to units larger than pairs; groups of individuals are matched in blocks (range of values)
Random assignment to groups from each block

Question 12

Advantages of between groups design (2)

Answer 12

1) Very simple design

2) No carryover effects

Question 13

Disadvantages of between groups design (3)

Answer 13

1) Requires many participants
2) Individual and environmental differences
3) Groups must be equivalent before manipulation