Chapter 9 - Within Groups design

Question 1

What is a within subjects design?

Answer 1

• Single group of participants

* Tests/observes each individual in all the different treatments being compared

Question 2

What is the other name of within subjects design?

Answer 2

Repeated Measures experimental design

Question 3

What are the 2 possible structures for a within subjects design?

Answer 3

Sequential: Treatments administered one after the other
Concurrent: Treatments administered all at once

Question 4

What are the 2 major sources of confounding in within subjects designs?

Answer 4

Enviromental variables and time-related variables

Question 5

What are environmental variables?

Answer 5

Characteristics of the environment that may change from one treatment to another

Question 6

What are time-related variables?

Answer 6

Factors influencing the participants between 1st and last measurements

Question 7

What are the confounding variables related to history?

Answer 7

environmental events other than the treatment that change over time and may affect the scores in one treatment differently than in another treatment
EX: life at home, school, work between the treatments

Question 8

What are the confounding variables related to maturation?

Answer 8

systematic changes in participants physiology/psychology that occur during a research study

Question 9

What are the confounding variables related to instrumentation?

Answer 9

changes in a measuring instrument that occur over time (mostly with behavioural observation measures)

Question 10

How is instrumentation also called?

Answer 10

instrumental bias or instrumental decay

Question 11

What is observer drift?

Answer 11

when observers become inconsistent in their observations (ex: becoming more strict or lenient in their categorization of behaviour)

Question 12

What are the confounding variables related to regression towards the mean?

Answer 12

tendency for extreme scores on any measurement to move toward the mean (regress) when the measurement procedure is repeated

Question 13

How is regression towards the mean also called?

Answer 13

Statistical regression

Question 14

What are order effects?

Answer 14

participation in one treatment has influence in participation in the following treatments
Any change in performance caused by participation in other treatments = order effects

Question 15

What is fatigue?

Answer 15

decline in performance as participant moves through treatments

Question 16

What is practice?

Answer 16

improvement in performance as participant gains experience through treatments

Question 17

What is carry-over?

Answer 17

effects on one treatment linger in the following treatment and affects its performance

Question 18

What are contrast effects?

Answer 18

type of carry over effect (EX: coming from a bright VS a dark room and entering a dimly lit room - perception will not be the same)

Question 19

What are progressive error effects?

Answer 19

Carry over effects are caused by experiencing other treatments, other effects (fatigue, practice) are called progressive error effects and are due to simply being in the study

Question 20

Name all time-related factors

Answer 20

History, maturation, instrumentation, regression

Question 21

Name all order effects

Answer 21

All effects directly relates to experience in other treatments

Question 22

What are the 3 methods to control for environmental factors?

Answer 22

• Randomization
• Holding constant
• Matching across treatments

Question 23

What are the 3 main ways to control for time related or order effects?

Answer 23

Controlling time
Switch to a betwee-subjects design
Counterbalancing

Question 24

What is controlling time?

Answer 24

Controlling the time it takes to complete the study (increases the potential of order effects)

Question 25

Why would we switch to a between subejcts design?

Answer 25

• If order, practice or fatigue effects are expected to be strong, it might be a good idea to switch to a between subjects design so that participants do not experience all treatments.

Question 26

What is counterbalancing?

Answer 26

• Changing the order of treatments between participants so that they don’t all develop experience/fatigue in the same order

Question 27

What is the effect of counterbalancing on order effects?

Answer 27

• Counterbalancing helps to minimize the difference in scores between 2 treatments due to order effects, but in real life studies, we can never know how important/impactful the order effects are compared to the effects of the treatments
Does not eliminate order effects; it distributes them

Question 28

What is the effect on counterbalancing on variance?

Answer 28

• Can increase variance within treatments (if half the scores receive a 5 points increase due to the counterbalancing in treatment 1, it obscures the true effect of treatment one)

Question 29

What is the absolute level of performance?

Answer 29

The true mean

Question 30

What are asymetrical order effects?

Answer 30

• We assume that order effects are the same for all treatments, but it might not be the case (one treatment might give more practice opportunity than another)
When this is the case, counterbalancing does not work well

Question 31

How can we calculate the numer of possible sequences depending on the number of treatments (n)?

Answer 31

n! (n factorial)

EX: if n=4, then n!=1x2x3x4=24 groups needed to go over each sequence

Question 32

What is complete counterbalancing?

Answer 32

When the researcher uses the same number of groups as the number of possible sequences of treatments in their experiment

Question 33

What is partial counterbalancing?

Answer 33

§ Each treatment occurs once 1st, once 2nd, once 3rd, etc…

For 4 treatments, we only need 4 sequences

Question 34

How can we determine which sequences to do or not do in partial counterbalancing?

Answer 34

Latin square:
1st row = ABCD
2nd row = D moves at the beginning (DABC)
Etc (CDAB,…)

Question 35

What are the advantages of within subjects designs

Answer 35

• Requires few participants in comparison to between-subjects
  
  • Eliminates the problem of individual differences (main concern of between subjects design)

Question 36

What are the 3 aspects to consider when choosing a within or between subjects experiment?

Answer 36

1. Individual Differences 
	Within Subjects eliminates this
2. Time-related factors and order effects
	Eliminated in Between Subjects
3. Fewer Participants
In within Subjects design

Question 37

What is a matched-subjects design?

Answer 37

• Uses a separate group for each treatment condition, but each individual in one group is matched to an individual in every other group (matching based on a variable crucial to the study)
• Goal: have all advantages of within and between subjects without the disadvantages

Question 38

What is a 2 treatment design?

Answer 38

Within subjects design with only 2 treatments

Question 39

How do we statistically analyze a two-treatment design?

Answer 39

• If data allows it, we can compute the 2 means for each group (then t test or ANOVA)
  
  • Ordinal/nominal variables - Wilcoxon Signed-Ranks test can be used to determine significance
  • Some within subjects only show the direction of the difference between the 2 treatments (sign test is used to determine if it’s significant)

Question 40

What is a multiple treatment design?

Answer 40

Within subjects with more treatments