Psych Methods 2314 B Sessions 5.1, 5.2, 5.3

Quasi-experimental design

The use of methods and procedures to make observations in a study that is structured similar to an experiment, but the conditions and experiences of the participants lack some control because the study lacks random assignment, includes a preexisting factor (i.e., a variable that is not manipulated), or does not include a comparison/control group.

Factorial designs are more informative than one-factor designs because:

They allow us to observe the interaction of two or more factors.

Three important reasons for adding factors to an experiment:

To build on previous data, To control for threats to validity, and To enhance the informativeness of interpretation

Using two-way factorial design, we can identify three sources of variation:

Two main effects, One interaction, and Error variance

A factorial experimental design includes the manipulation of

Two or more independent variables

How are the conclusions we can draw in a factorial design limited when the design includes at least one quasi-independent factor?

We do not show cause and effect for any effect that involves the quasi-independent factor.

Complete factorial design/completely crossed design

a factorial design in which each level of one factor is combined or crossed with each level of the other factor, with participants observed in each cell or combination of levels.

participant variable

a quasi-independent or preexisting variable that is related to or characteristic of the personal attributes of a participant; typically are demographic characteristics like intelligence level, age, gender, race, ethnicity, education level, personality type, and body weight.

Factorial experimental design

a research design in which groups are created by manipulating the levels of two or more factors, then the same or different participants are observed in each group using experimental procedures of randomization (for a between-subjects factor) and using control for timing and order effects (for a within-subjects factor).

Factorial design

a research design in which participants are observed across the combination of levels of two or more factors.

Two-way factorial design

a research design in which participants are observed in groups created by combining or crossing the levels of two factors

Main effect

a source of variation associated with mean differences across the levels of a single factor. in a table summary, it is the measure of how the row and column means differ across the levels of a single factor

two-way ANOVA

a statistical procedure used to analyze the variance in a dependent variable between groups created by combining the levels of two factors and used for data that are measured on an interval or ratio scale

An effect of a quasi-independent variable shows that the factor is related to changes in a __________ ____________. It does not demonstrate cause and effect because the factor is _________________.

dependent variable, preexisting

When at least one factor in a factorial design is manipulated (an independent variable), the design is typically called an ______________, even if a quasi-independent variable is included in the design.

experiment

In a two-way factorial design, there are two main design effects: one for ___________ __ and one for ____________ __.

factor A, factor B

In a ____________ design, the levels of both factors must be manipulated, and experimental procedures must be used to assign or observe participants in each group.

factorial

The need to ease the burden on the participants is especially important for a _____________ design because the number of groups created by combining the levels of at least two factors can be large.

factorial

To control for threats to internal validity, these threats can be included as _________ in a factorial design.

factors

An ___________ can be identified in the cell means of a table summary.

interaction

Only a factorial design can demonstrate an _______________ effect.

interaction

The change in a dependent variable across the combined levels of two factors is called an ______________.

interaction

A ____________ effect can be identified in the row means and column means of a table summary.

main

Factorial designs are more informative in that they allow us to ___________ the interaction of two or more factors.

observe

The variance attributed to error in a factorial design is associated with differences in ___________ within each cell.

participant scores

When all factors in a factorial design are ______-____________, the design is not an experiment because no factor was manipulated.

quasi-experimental

Factorial designs allow you to build on previous research by ________________ a previous result while also ________________ a new result in the same design.

replicating, demonstrating

A ________________ interaction indicates that group means significantly vary across the combined levels of two factors.

significant

To compute the test statistic, we divide the ____________ between groups by the variance attributed to _________ for each main effect test and the interaction.

variance, error

Two concerns are of particular importance for a factorial design:

1) The larger the number of levels combined to create the groups, the greater the demands on the participants, and 2) the greater the demands in each group, the greater the burden on the participants

If we have two levels of a factor, we will have 2 x 2 = ___ groups

4

Between-subjects design

A research design in which different participants are observed one time in each group or at each level of a factor.

Mixed-factorial design

A research design in which participants are observed at each level of a between-subjects factor and also repeatedly observed across the levels of the within-subjects factor.

Within-subjects design

A research design in which the same participants are observed one time in each group of a research study.

Interaction

A source of variation associated with how the effects of one factor are influenced by, or depend on, the levels of a second factor. In a table summary, it is a measure of how cell means at each level of one factor change across the levels of a second factor.

Main effect

A source of variation associated with mean differences across the levels of a single factor.

Quasi-independent variable

A variable with levels to which participants are not randomly assigned and which differentiates the groups or conditions being compared in a research study. Because the levels of the variable are preexisting, it is not possible to randomly assign participants to groups.

A researcher conducts a 4 x 2 factorial design with 10 participants observed in each group. How many participants are needed to conduct this experiment if the researcher conducts: a) A between-subjects factorial design, a b) within-subjects factorial design, a c) mixed factorial design in which the first variable is a within-subjects factor, and d) a mixed factorial design in which the second variable is a within-subjects factor?

A) 80 participants, B) 10 participants, C) 20 participants, and D) 40 participants

Three types of factorial designs:

Between-subjects, Within-subjects, Mixed-factorial designs

For a 2 x 2 factorial design, we manipulate the levels of each factor, thereby creating ________ unique groups

Four

A researcher manipulates the type of color used in a product line (bright, dark) and tests if preference ratings for the product vary by gender (man, woman). In this example, the quasi-independent participant variable is:

Gender

A researcher measures the intensity of an exercise among lean and obese students who are randomly assigned to exercise with a fit or unfit confederate. Which of these factors are quasi-independent factors?

Health (lean, obese).

A researcher tests the effectiveness of couple's therapy (individual, group) for each spouse (husband, wife). The results show that for both spouses, group therapy is most effective. What effect was described in this example?

Main effect of Therapy.

For the mixed factorial design to be an experiment, the researchers must

Manipulate the levels of each factor, Cross the levels of the two factors to create the groups, Randomly assign different participants to each level of the between-subjects factor, and Control for order effects due to observing the same participants at each level of the within-subjects factor

For the within-subjects factorial design to be an experiment, the researchers must

Manipulate the levels of each factor, Cross the levels of the two factors to create the groups, and Control for order effects due to observing the same subjects in each group or in each environment

For the between-subjects factorial design to be an experiment, the researchers must

Manipulate the levels of each factor, Cross the levels of the two factors to create the groups, and Randomly assign different participants to each group

A researcher measures student enthusiasm in a class that varies by size of the room (small, large) and number of students (few, many). The results show that enthusiasm in class was greatest in a small room with few students. However, when the room was large, enthusiasm was greatest with many students. What effect was described in this example?

Room size × Number of student's interaction.