Social Research Methods: Qualitative and Quantitative Approaches

STRATEGIES OF RESEARCH DESIGN

is the independent variable. The variable that is
the effect, result, or outcome of another variable
is the dependent variable. The independent vari-
able is “independent of” prior causes that have
acted on it whereas the dependent variable depends
on the cause.
It is not always easy to determine whether a
variable is independent or dependent. Two ques-
tions can help to identify the independent variable.
First, does it come before other variables in time?
Independent variables must come before any other
type. Second, if two variables occur at the same
time, does one variable have an impact on another
variable? Independent variables affect or have an
impact on other variables. We often phrase research
topics and questions in terms of the dependent
variable because dependent variables are the phe-
nomena we want to explain. For example, an exam-
ination of the reasons for an increase in the crime
rate in Dallas, Texas would have the dependent
variable as the crime rate in Dallas.
A simple causal relationship requires only an
independent and a dependent variable. A third vari-
able type, the intervening variable, appears in
more complex causal relations. Coming between
the independent and dependent variables, this vari-
able helps to show the link or mechanism between
them. Advances in knowledge depend not only on
documenting cause-and-effect relationships but
also on specifying the mechanisms that account for
the causal relation. In a sense, the intervening vari-
able acts as a dependent variable with respect to the
independent variable and acts as an independent
variable toward the dependent variable.
For example, French sociologist Émile Durk-
heim developed a theory of suicide that specified a
causal relationship between marital status and sui-
cide rate. Durkheim found evidence that married
people are less likely to commit suicide than single
people. He believed that married people have more
social integration (i.e., feelings of belonging to a
group or family). He thought that a major cause of
one type of suicide was that people lacked a sense
of belonging to a group. Thus, his theory can be
restated as a three-variable relationship: marital sta-
tus (independent variable) causes the degree of
social integration (intervening variable), which

affects suicide (dependent variable). Specifying

the chain of causality makes the linkages in a

theory clearer and helps a researcher test complex

explanations.^15

Simple theories have one dependent and

one independent variable whereas complex ones

can contain dozens of variables with multiple

independent, intervening, and dependent vari-

ables. For example, a theory of criminal behavior

(dependent variable) identifies four independent

variables: an individual’s economic hardship,

opportunities to commit crime easily, membership

in a deviant subgroup that does not disapprove of

crime, and lack of punishment for criminal acts.

A multicause explanation usually specifies which

independent variable has the most significant

causal effect.

A complex theoretical explanation has a string

of multiple intervening variables. For example, fam-

ily disruption causes lower self-esteem among chil-

dren, which causes depression, which causes poor

grades in school, which causes reduced prospects

for a good job, which causes a lower adult income.

The chain of variables is family disruption (indepen-

dent), childhood self-esteem (intervening), depres-

sion (intervening), grades in school (intervening), job

prospects (intervening), adult income (dependent).

Two theories on the same topic can differ as to

the number of independent variables. In addition,

theories might agree about the independent and

dependent variables but differ on the intervening

variable or causal mechanism. For example, two

theories say that family disruption causes lower

adult income, each for different reasons. One theory

Independent variable A type of variable that pro-

duces an effect or results on a dependent variable in a

causal hypothesis.

Dependent variable The effect or result variable

that is caused by an independent variable in a

causal hypothesis.

Intervening variable A variable that comes logi-

cally or temporally after the independent variable

and before the dependent variable and through

which their causal relation operates.