Experimental Designs: Between and Within Subjects Design: Chapter 8 & 9

Question 1

between groups

Answer 1

• 2+ groups are formed at random from a
  pool of subjects
• each group receives a different experimental treatment (value of the IV)
• scores for the groups are
  compared

Question 2

between groups: obtaining results

Answer 2

• 1 score per individual
• these are independent measures

Question 3

do scores vary within groups

Answer 3

yes

Question 4

systematic variance

Answer 4

difference in the DV

Question 5

looking for an effect of IV

Answer 5

to look for an effect of IV, compare mean scores (DV) for each group

Question 6

determining statistical significance

Answer 6

compare between groups variance to within groups variance
F = between-group variance / within group variance

Question 7

When there is a large within-group variance, it is
difficult to see an effect, we want to ____

Answer 7

minimize it

Question 8

large versus small variance in groups

Answer 8

• large variance in between groups (BG) = good
• large variance in within groups (WG) = bad

Question 9

keeping within group variance low

Answer 9

limit individual differences
- Standardizing procedures
- Holding a participant variable constant
- Increase sample size

Question 10

individual differences in between-groups are usually ____

Answer 10

always a potential confounding variable for this design

Question 11

making between groups as equal as possible

Answer 11

• created equally
• treated equally, except for IV
• composed of equivalent individuals

Question 12

randomization

Answer 12

• participants randomly assigned to groups to
  ensure groups are as equal as possible before
  treatment or intervention
• most powerful technique to control for the effect
  of pre-existing differences

Question 13

randomization vs random sampling

Answer 13

randomization:
- random assignment of Ss to experimental
or control groups in a particular study
random sampling:
- random selection of Ss from a larger
population to participate in a study

Question 14

free random assignment

Answer 14

• groups are based on chance
• if 2 groups +, table of random numbers is used to guard against repetition
• should lead to equality, but no guarantee

Question 15

randomization: matched group

Answer 15

• participants matched on critical variables that may act as important confounds
• inherent in within-groups designs.
• ex:
  1. intelligence
  2. gender
  3. age
  4. severity of illness

Question 16

randomization: randomized blocks

Answer 16

groups of individuals are matched in blocks

Question 17

matched groups

Answer 17

critical variables that can act as confounds
- intelligence
- gender
- age
- severity of illness

Question 18

matching procedure

Answer 18

1. Rank subjects on the variable for which
   control is desired. May require pretest.
2. Segregate subjects into matched pairs
   on that variable.
3. Randomly assign pair-members to the
   conditions.

Question 19

advantages of between-groups

Answer 19

• very simple design
• no carryover effects

Question 20

disadvantages of between-groups

Answer 20

• requires many participants
• individual differences & environmental differences
• groups must be equivalent before the manipulation

Question 21

within-groups design

Answer 21

• only one treatment group and each subject is
  given all levels (or conditions) of the IV
• comparison = between scores obtained at
  different levels of the IV for same participants
• each participant serves as their own control

Question 22

categories of within-groups

Answer 22

• concurrent measures
• repeated measures

Question 23

concurrent measures

Answer 23

• all levels of IV are present at the same time – choice paradigm
• subjects choose the value of the IV they prefer

Question 24

Harlow: monkeys cloth mother
(comfort) versus wire mother
(food).
Measured time spent at
each mother.
This is an example of ______

Answer 24

concurrent measures

Question 25

repeated measures

Answer 25

• most common approach for within-subjects
• every subject receives all values of the IV
• participant’s performance is the basis of comparison

Question 26

what does the repeated measures accomplish

Answer 26

1. equating groups (by using same participants)
2. reducing within-group variance (by controlling
   for individual differences)

Question 27

advantages of repeated measures

Answer 27

• increases sensitivity
• increases ability to detect a treatment
  effect
• error variance is reduced considerably because the participants become their own control (individual differences are eliminated)

Question 28

main issue with repeated measures: carryover effects

Answer 28

• effects that one treatment may have on another treatment
• includes: practice effects, fatigue, boredom,
  interference
• exposure to one manipulation may produce consequences influencing response to manipulations

Question 29

solutions to carryover effects

Answer 29

• randomization
• counterbalancing

Question 30

counterbalancing

Answer 30

• all possible treatment orders are used equally
• equal numbers of participants in each treatment condition

Question 31

counterbalancing: examples

Answer 31

2 treatments
- 2 x 1
3 treatments
- 3 x 2 x 1
4 treatments
- 4 x 3 x 2 x 1
product is the total amount of combinations

Question 32

latin square design

Answer 32

• each treatment (A, B, C & D) occurs equally often in each position in the experiment
• refer to chapter 8&9, slide 32

Question 33

reversibility in within-groups

Answer 33

• within-subjects designs = not adequate IF experimental conditions produce lasting effect on
  the participant (cannot be reversed).
• IVs permanently alter the development or state
  of participants
• have irreversible carry-over effects

Question 34

examples of irreversible carryover effects

Answer 34

• physiological damage (brain lesions)
• interventions that improve or worsen a skill, such as learning or memory
• habituation

Question 35

reversal design: ABA design

Answer 35

• allows verifying the presence/absence
  of carry-over effects
  Condition A = measure behavior at baseline
  Condition B = measure during intervention
  Condition A = measure after intervention stopped

Question 36

Does behaviour return to the baseline?

Answer 36

YES: no carryover effect
NO: carryover effect

Question 37

carryover effect desirability

Answer 37

• carryover effect can be desirable

Question 38

advantages of within groups

Answer 38

• fewer participants required
• greater sensitivity to treatment effect (elimination individual differences)
• good when participants are hard to find
• each participant acts as his own control
• powerful design under suitable conditions

Question 39

disadvantages of within groups

Answer 39

• not suitable when carryover effects are permanent
• participant attrition may be a problem