Chapter 8 - Experimental Design

Question 1

Between-Subjects Design

Answer 1

A study in which individuals are assigned to only one treatment or experimental condition and each person provides only one score for data analysis

Question 2

Within-Subjects Design

Answer 2

An experimental design in which the effects of treatments are seen through the comparison of scores of the same participant observed under all the treatment conditions

Question 3

Sampling Bias

Answer 3

A systematic and directional error involved in the choice of units, cases, or participants from a larger group for study

Question 4

Selection Differences

Answer 4

A form of sampling bias in which participants in different conditions vary in a systematic way from each other

Question 5

Posttest Design

Answer 5

An assignment carried out after the application of some intervention, treatment or other condition to measure any changes that have occurred

Question 6

Pretest Posstest Design

Answer 6

A research design in which the same assessment measures are given to participants both before and after they have received a treatment or been exposed to a condition, which such measures used to determine if there are any changes that could be attributed to the treatment or condition

Question 7

Advantages and Disadvantages of a Pretest

Answer 7

Advantages
- To alleviate problems associated with a small sample size because we can ensure even small samples are equivalent on a variable
- To select appropriate participants on a variable of interest
- To combat selective attrition, wherein certain participants leave the study in a systematic way

Disadvantages
- It can sensitize participants to the experiment and therefore generate demand characteristics

Question 8

Matched Pairs Design

Answer 8

A study involving two groups of participants in which each member of one group is paired with a similar person in the other group, that is, someone who matches them on one or more variables that are not the main focus of the study but nonetheless could influence its outcome.

Pros:
- Small sample size; harder to create equivalent groups
- Helps remove some variability between groups
Cons:
- Cost & time for researchers and participants

Question 9

Comparing Pretest Posttest and Matched Pairs Designs

Answer 9

Pretest Posttest Design: the equivalence on some characteristic of the sample can be determined post hoc. However, the purpose is to compare the effect of the intervention.

Matched Pairs Design: the equivalence on some characteristic of the sample, usually demographic, is determined a priori.

Question 10

Within-Subjects Design

Answer 10

An experimental design in which the effects of treatments are seen through the comparison of scores of the same participant observed under all the treatment conditions.

Question 11

Demand Characteristics

Answer 11

Cues that may influence or bias participants’ behavior, for example, by suggesting the outcome or response that the experimenter expects or desires.

Question 12

Order Effect

Answer 12

The influence of the order in which treatments are administered, such as the effect of being the first administered treatment (rather than the second, third, and so forth).

As individuals participate in first one and then another treatment condition, these conditions could affect the participants’ responses and confound the results of the study.

There are many forms of order effects.

Question 13

Practice Effect

Answer 13

Any change or improvement that results from practice or repetition of task items or activities.

Question 14

Fatigue Effect

Answer 14

A decline in performance on a prolonged or demanding research task that is generally attributed to the participant becoming tired or bored with the task.

Question 15

Contrast Effect

Answer 15

When participants’ responses in a later condition are affected by a particular experience they had in an earlier condition.

Question 16

Counterbalancing

Answer 16

Arranging a series of experimental conditions or treatments in such a way as to minimize the influence of extraneous factors

Question 17

Partial Counterbalancing (Latin-Square)

Answer 17

Latin-Square Design: a type of within-subjects design in which treatments, denoted by Latin letters, are administered in sequences that are systematically varied such that each treatment occurs equally often in each position of the sequence (first, second, third, etc.).

(Picture in doc)

Question 17

Partial Counterbalancing (Latin-Square)

Answer 17

Latin-Square Design: a type of within-subjects design in which treatments, denoted by Latin letters, are administered in sequences that are systematically varied such that each treatment occurs equally often in each position of the sequence (first, second, third, etc.).

Question 18

Time Interval

Answer 18

Another technique to deal with order effects: allowing time to pass between the presentation of conditions.

A rest period could counteract a fatigue effect, while an unrelated task may counteract a contrast effect.

Question 19

Between-Subject Design vs Within-Subjects Design

Answer 19

Between-Subjects Design
- Less likely to violate internal validity due to order effects
- Participants are less likely to exhibit demand characteristics

Within-Subjects Design
- Fewer participants are required
- Easier to detect differences between conditions because we can remove error variance associated with participant characteristics
- Order, practice, fatigue, and contrast effects limit internal validity
- Introduces demand characteristics