Ch. 9: Experimental Designs: Within-Subjects Design

Question 1

synonym of within-subjects design

Answer 1

repeated-measures design

Question 1

goal of within-subjects design

Answer 1

Use a single group of participants and test or observe each individual in all of the different treatments being compared

Question 2

how are treatments administered in within-subjects designs?

Answer 2

The treatments can be administered sequentially or all together

Question 3

groups in treatment conditions in within-subjects designs

Answer 3

are equivalent to the group in every other condition

Question 4

within-subjects designs in nonexperimental research

Answer 4

they are well-suited to nonexperimental research that investigates changes occurring over time

Question 5

two main threats to internal validity of within-subjects experiments

Answer 5

confounding from environmental variables and time-related variables

Question 6

types of confounding from time-related variables

Answer 6

• history
• maturation
• instrumentation
• regression toward the mean
• order effects

Question 7

history

Answer 7

the environmental events other than the treatment that change over time and may affect the scores in one treatment differently than another treatment

Question 8

maturation

Answer 8

any systematic changes in participants’ physiology or psychology that occur during the research study and affect the participants’ scores

Question 9

when is maturation particularly a concern?

Answer 9

for young children or elderly adults

Question 10

instrumentation

Answer 10

changes in a measuring instrument that occur over time

Question 11

when is instrumentation particularly a concern?

Answer 11

with behavioural observation measures

Question 12

regression toward the mean

Answer 12

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

Question 13

why does regression toward the mean occur?

Answer 13

because an individual’s score is a function of stable factors and unstable factors, which change substantially from one measurement to another

Question 14

order effects

Answer 14

occur when the experience of being tested in one treatment condition has an influence on participants’ scores in later treatment conditions

Question 15

types of order effects

Answer 15

• carry-over effects
• contrast effects
• progressive error
• fatigue effesct
• practice effects

Question 16

carry-over effects

Answer 16

occur when one treatment condition produces a change in participants that affects their scores in subsequent treatment conditions

Question 17

contrast effect

Answer 17

the subjective perception of a treatment condition is influenced by its contrast with the previous treatment

Question 18

progressive error

Answer 18

refers to changes in participants’ behaviour or performance that are related to experience but not specific treatment

Question 19

examples of progressive error

Answer 19

Practice effects and fatigue

Question 20

fatigue effects

Answer 20

progressive decline in performance as a participant works through a series of treatment conditions

Question 21

practice effects

Answer 21

progressive improvement in performance as a participant gains experience through the series of treatment conditions

Question 22

how can environmental factors be controlled?

Answer 22

Randomization
Holding them constant
Matching across treatment conditions

Question 23

how can treatment effects be controlled?

Answer 23

Controlling time
Switching to a between-subjects design
Counterbalancing

Question 24

controlling time

Answer 24

- The possibility that a study will be affected by a time-related threat is directly related to the length of time required to complete the study - Shortening the time between treatments can reduce the risk of time-related threats - But, this can increase the likelihood that order effects will influence the results

Question 25

switching to a between-subjects design

Answer 25

In some situations, order effects are so strong that a researcher wouldn’t even consider using a within-subjects design

Question 26

counterbalancing

Answer 26

changing the order in which treatment conditions are administered from one participant to another so that the treatment conditions are matched concerning time

Question 27

goal of counterbalancing

Answer 27

to use every possible order of treatments with an equal number of individuals participating in each sequence

Question 28

purpose of counterbalancing

Answer 28

to eliminate the potential for confounding by disrupting any systematic relationship between the order of treatments and time-related factors

Question 29

how is counterbalancing usually discussed?

Answer 29

in terms of order effects, but it has the same effect on time-related threats

Question 30

limits of counterbalancing

Answer 30

- It does not eliminate order effects entirely - It adds the order effects to some of the individuals within each treatment, but not to all of the individuals - It assumes symmetry of order effects, which isn’t always justified - It is necessary to present the treatments in every possible sequence to completely counterbalance - As the number of treatments increases, counterbalancing becomes more complex

Question 31

how is the number of different treatment conditions identified?

Answer 31

as n! (n factorial)

Question 32

solution to complex counterbalancing

Answer 32

use partial counterbalancing

Question 33

partial counterbalancing

Answer 33

uses enough different orderings to ensure that each treatment condition occurs first in the sequence for one group of participants, second for another group, third in another group, and so on

Question 34

latin square

Answer 34

a simple and unbiased procedure for selecting sequences that involves creating an n x n matrix and filling it with letters

Question 35

advantages of within-subjects designs

Answer 35

- It requires relatively few participants - It eliminates all problems based on individual differences - Reduces variance - More statistically powerful: it reveals treatment effects that might not be apparent in a between-subjects design

Question 36

disadvantages of within-subjects designs

Answer 36

- There is an opportunity for time-related factors to influence participants’ scores - Participant attrition

Question 37

participant attrition

Answer 37

some of the individuals who start the research study may be gone before the study is completed

Question 38

three main factors that differentiate within- and between-subjects designs

Answer 38

individual differences time-related differences number of participants

Question 39

individual differences and choosing within- or between-subjects design

Answer 39

if you anticipate large individual differences, it is better to use a within-subjects design

Question 40

time-related factors and order effects and choosing within- or between-subjects design

Answer 40

if you expect one or more treatment condition(s) to have large and long-lasting effects that may influence participants in future conditions, it is better to use a between-subjects design

Question 41

fewer participants and choosing within- or between-subjects design

Answer 41

whenever it is difficult to find or recruit participants, a within-subjects design is better

Question 42

matched-subjects design

Answer 42

each individual in one group is matched with a participant in each of the other groups.

Question 43

how is matching done in matched-subjects designs?

Answer 43

so that the matched individuals are equivalent concerning a variable that the researcher considers to be relevant to the study

Question 44

goal of matched-subjects designs

Answer 44

to duplicate all advantages of within- and between-subjects designs without the disadvantages of either one

Question 45

advantages of matched subjects

Answer 45

- There are no order effects - It removes the variance caused by individual differences

Question 46

disadvantage of matched-subjects designs

Answer 46

matching can become very difficult as the number of matched variables increases and the number of different groups increases

Question 47

two main applications of within-subjects designs

Answer 47

Two-treatment designs Multiple-treatment designs

Question 48

two-treatment designs

Answer 48

Within-subjects help evaluate the difference between two treatment conditions

Question 49

advantages of two-treatment designs

Answer 49

- It is easy to conduct - Increases the likelihood of obtaining a significant difference - It is easy to counterbalance

Question 50

disadvantages of two-treatment designs

Answer 50

- It only provides two data points - Does not provide any indication of the functional relationship between the independent and dependent variables

Question 51

statistical analyses for two-treatment designs

Answer 51

- In cases with two treatment conditions, a repeated-measures t-test or a single-factor ANOVA (repeated measures) can determine the statistical significance - If the data are on an ordinal scale, a Wilcoxon Signed-Ranks test can be used

Question 52

directionality and two-treatment designs

Answer 52

- Occasionally, a within-subjects study only produces data that shows the direction of the difference between the two treatments - In this situation, you can statistically evaluate the data using a sign test

Question 53

advantage of multiple-treatment designs

Answer 53

You are more likely to reveal the functional relationship between the two variables being studied

Question 54

disadvantages of multiple-treatment designs

Answer 54

- With too many conditions, the distinction between treatments may become too small to generate significant differences in behaviour - Multiple treatments increase the amount of time required for each participant to complete the full series of treatments, increasing participant attrition - Counterbalancing becomes more difficult

Question 55

statistical analyses for multiple-treatment designs

Answer 55

With data on an interval or ratio scale, repeated-measures ANOVA is typically used