Chapter 9 & 10 - Between-Subjects & Factorial Designs

What is a between-subjects design?

Different groups of participants are randomly assigned to different levels of the IV.

ex: Group A gets Drug A; Group B gets Drug B

What is a within-subjects design?

The same group of participants is exposed to all levels of the IV

ex: everyone receives both drug a and drug b

what is a mixed-factor design

a design containing both between and within-subjects factors

what is a single subject design

a single participant or small group is exposed to all levels of the IV, and behavior is evaluated individually rather than averaged

what is a single-factor randomized groups design

an experiment with one The same group of participants is exposed to all levels of the IV, where participants are randomly assigned to its levels

what is a randomized two-group design

a between-subjects design with 2 levels of one IV

what is a two-experimental-group design

A design comparing two different treatment levels, with neither necessarily being a no-treatment control.
Ex: 5 mg vs. 10 mg of a drug.

What is an advantage of a two-group design?

It is simple, requires fewer participants, and is relatively easy to analyze

What is a disadvantage of a two-group design?

It provides limited information about the relationship between the IV and DV

What is a multiple-groups design?

A design in which an IV has more than two levels

Why use a multiple-groups design instead of only two groups?

It provides a more complete understanding of treatment effects

What is a parametric design?

Different IV levels represent quantitative differences.
Ex: 0, 5, and 10 mg of a drug.

What is a nonparametric design?

Different IV levels represent qualitative differences.
Ex: Male vs. female

What is the main disadvantage of adding more treatment groups?

It requires more participants, materials, time, and money

What is a representative sample?

A sample that closely matches the characteristics of the population

What is a convenience sample?

A sample selected from groups that are easy or convenient to access

What is stratified sampling?

Dividing the population into demographic groups (strata) and randomly sampling from each.

ex: Randomly sample men and women separately

What is proportionate sampling?

Stratified sampling where the proportions of groups in the population are reflected in the sample

ex: Sample 60% women, 40% men to match population

What is a matched-groups design?

Participants are matched on characteristics related to the DV, then randomly assigned to different groups.
Ex: Pair people with similar IQ scores

What is the purpose of matching participants

to reduce error variance and potentially increase the ability to detect an effect

What are three methods of matching participants?

1. precision matching

2. range matching

3. rank-order matching

What is the main disadvantage of matched-groups designs?

They require a large pool of participants, may result in data loss, and you cannot anticipate every possible confounding variable

what is error variance

Variability in scores that is not caused by the independent variable.
Ex: Differences in participants' attention

what are three sources of error variance

1. individual differences

2. environmental conditions

3. changes in participants physical or mental states

How can researchers reduce error variance?

Hold extraneous variables constant, match participants, randomly assign participants

What is a factorial design?

A design with two or more independent variables (factors). It allows researchers to examine main effects and interactions.

What are main effects and interactions in a factorial design?

A main effect is the separate effect of one IV.

An interaction occurs when the effect of one IV changes depending on the level of another IV.

Example: A drug works better in the morning than at night → interaction between drug dosage and time of day.