A Variable is any characteristic or quality that varies
among the members of a particular group
Example: gender, eye color, motivation..
The individual members or class of objects however
should differ-or vary- to qualify the class as a variable.
A constant is a characteristic or quality that is the
same for all members of a particular group.
Example: A researcher is interested in studying
the effects of reinforcement on student
• Quantitative variables: varies in amount and
degree but not in kind
Example: height, length, interest
• Categorical variables: varies only in kind, not in
degree or amount (qualitatively different).
Example :eye color, gender, occupation.
Types of variables:
Researchers in education often study the
1. Two or more quantitative variables
Ex: -Reading achievement and
- Amount of time watching
television and aggressiveness of
2. One categorical and one quantitative
Ex: -Method used to teach reading and
-Counseling approach and level of
3. Two or more categorical variables
Ex: -Gender of teacher and subject
- Ethnicity and father occupation
N.B: Some variables can be treated both as
quantitative or categorical
EX: quantitative :degree of anxiety level
Categorical : group of high anxiety/Group of low
• An independent variable is presumed to
influence other variables. Sometimes
independent variables are called
manipulated variables or experimental
• An independent variable may be either manipulated
– A manipulated variable is produced by the
Ex: amount of reinforcement
– A selected variable is one that already exists and
that the researcher locates and then chooses to
Ex: Gender, mathematical ability, test anxiety
• A dependent variable is presumed to be affected by
one or more independent variable. The dependent
variable is often called an outcome variable
Example: Gender of teacher and subject matter
• A moderator variable is a secondary
independent variable that the researcher
selects because he or she thinks it may
affect the relationship between the primary
independent variable and the dependent
• Research Question 1: “Does anxiety affect
test performance and, if so, does it depend on
– Independent variable: anxiety level
– Moderator variable: test-taking experience
– Dependent variable: test performance
A mediator variable is a variable that attempts to
Explain the relationship between the 2 variables.
Example : “Does anxiety affect test performance
and, if so, does it depend on test-taking
The mediator could be the SES
• An extraneous variable is an independent
variable that may have unintended effect on
the dependent variable.
The principal of a high school compares the final
examination scores of two history classes taught by
teachers who use different methods, not realizing that
they are also different in many other ways because of
The classes differ in:
Size of class - Gender of students- Gender of teacher-
Age of teacher - Time of day class meets
Days of week class meets- Length of class - Ethnicity of
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