Department

Psychology

Course Code

PSYB01H3

Professor

Anna Nagy

Chapter 10 â€“ Complex Experimental Design

Increasing the Number of Levels of an Independent Variable

â€¢In the simplest experimental design there are only two levels of the

independent variable

â€¢However, a researcher may want to design an experiment with three or more

levels for several reasons:

1. A design with only two levels cannot provide very much info about the

exact relationship. Eg look at example 10.1 on page 187. It illustrates

how a relationship can go from a positive linear relationship to a

monotonic positive relationship by adding levels.

2. an experimental design with only two levels of the independent

variable cannot detect curvilinear relationships (recall form chapter 4 â€“

in a curvilinear relationship the relationship between variables changes

and sot he graph changes direction at least once). If a curvilinear

relationship is predicted, at least three levels must be used. For

example, the relationship between fear arousal and performance â€“ may

such relationship exist in psychology!

3. Researchers are often interested in comparing more than two groups.

For example, when comparing the effect of playing with animals on

elderly people, they may want to test the difference between playing

with a dog, playing with a cat, playing with a bird, or playing with no

animal at all.

Increasing the Number of Independent Variables: Factorial Designs

â€¢Researchers often more than one independent variable in a single experiment, -

typically 2 or 3 independent variables are operating simultaneously, which is a

closer approximation of real-world conditions in which independent variables do

not exist by themselves

â€¢In any given situation a number of variables are operating to affect behaviour â€“ eg

the experiment in which both the crowding and the windows were effecting the

cognitive performance of participants

â€¢It is possible to design an experiment with more than one independent variable

â€¢Factorial Designs are designs with more than one independent variable or factor

â€¢In a factorial design, all levels of each independent variable are combined with all

levels of the other independent variables

â€¢In the simplest factorial design, known as a 2 x 2 (two by two) factorial design â€“

there are two independent variables each with two levels

â€¢In a study by Ellesworth, a 2 x 2 design was used. They studied the effects of

asking misleading questions on the accuracy of eyewitness testimony. The second

independent variable was the questionerâ€™s knowledge of the crime: either they

were knowledgeable or naÃ¯ve. This 2 x 2 design resulted in 4 experimental

conditions:

www.notesolution.com

1. knowledgeable questioner â€“ misleading questions

2. knowledgeable questioner â€“ honest questions

3. naÃ¯ve questioner â€“ misleading questions

4. naÃ¯ve questioner â€“ honest questions

â€¢the general format for describing a factorial design is:

Nuber of levels x Number of levels x Number of levels

of first IV of second IV of third IV

and so on

â€¢a design with three two independent variables, one with two levels and one with

three levels would have a 2 x 3 factorial design. There are therefore six conditions

in the design.

Interpretation of Factorial Designs

â€¢Factorial designed yield two types of info:

1. the effect of each independent variable taken by itself. This is known as

the main effect of an independent variable. In a design with two

independent variables, there are two main effects, one for each

independent variable

2. interaction â€“ if there is interaction between two independent variables,

the effect of one independent variable depends of the particular level of

the other variable. In other words, the effect that one independent variable

has on a dependent variable depends on the level of the other independent

variable. To illustrate main effect and interaction, look at table 10.1 on

page 190 which illustrates a common method of presenting both outcomes

â€“ the number in each cell is the mean percent of errors made in the four

conditions of the experiment

Main Effects

â€¢the main effect is the effect each variable has by itself.

â€¢The main effect of each independent variable is the overall relationship between

the independent variable and the dependent variable.

â€¢Good explanation of chart 10.1 on pg 190

Interactions

â€¢These main effects tell us that overall there are more errors when the questioner is

knowledgeable and when the questions are misleading, but there is also the

possibility that an interaction exists; if so, the main effects of the independent

variables must be qualified because an interaction between independent variables

indicated that the effect of one independent variable is different at different at

different levels of the other independent variable

www.notesolution.com

Over 90% improved by at least one letter grade.

OneClass has been such a huge help in my studies at UofT especially since I am a transfer student. OneClass is the study buddy I never had before and definitely gives me the extra push to get from a B to an A!

Leah â€” University of Toronto

Balancing social life With academics can be difficult, that is why I'm so glad that OneClass is out there where I can find the top notes for all of my classes. Now I can be the all-star student I want to be.

Saarim â€” University of Michigan

As a college student living on a college budget, I love how easy it is to earn gift cards just by submitting my notes.

Jenna â€” University of Wisconsin

OneClass has allowed me to catch up with my most difficult course! #lifesaver

Anne â€” University of California

Join OneClass

Access over 10 million pages of study

documents for 1.3 million courses.

Sign up

Join to view

OR

By registering, I agree to the
Terms
and
Privacy Policies

Already have an account?
Log in

Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.