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Not only did Fisher practically invent a powerful, elegant, and relatively
simple experimental procedure, he produced the statistical technique to
analyze the data collected through such a procedure. This technique was
the ANOVA as well as the analysis of covariance (ANCOVA). He laid the
groundwork and documentation for this work as well as the experimental
design innovations through a series of what are now considered to be
classic publications (Fisher, 1921b, 1925, 1935; Fisher & Eden, 1927; Fisher
& Mackenzie, 1923). This analytic technique of ANOVA has now become
the foundation of entire curricula in research methods courses in the social
and behavioral sciences and is the focus of this topic.
1.3 DEPENDENT AND INDEPENDENT VARIABLES
ANOVA is a statistical technique that is applied to a data set. These data
may have been collected in either an experimental or nonexperimental
manner, but in performing the ANOVA it is essential that the researchers
have identified which variables are assigned the roles of the dependent
and independent variables.
1.3.1 THE CONCEPT OF A VARIABLE
A variable is anything that can take on different values. According to this
definition, almost everything that is a part of our world is a variable. To
name just three examples, the speed with which we drive down the street,
the intensity of our caring for another person, and the color of our hair
are all variables. This is because we can drive down the street at 10, 15, or
25 miles per hour; we can care for another somewhat, a moderate amount,
or considerably; and our hair color can be blond, brown, black, or grey.
1.3.2 DEPENDENT VARIABLE
Dependent variables
or
dependent measures
reflect the outcome of the
study, and a useful way to conceptualize them is as
outcome variables
or
outcome measures
.IntheexampleweusedinSection1.1,theresponsesto
the mood questions were the dependent variable in the study. Participants
answered the questions according to their own individual feelings, and so
the numerical values we would obtain from them could take on a range
of possible values. In other research studies, dependent variables could be
the number of patients in a particular category (e.g., females who have
contacted a medical provider for a flu vaccination), the number of words
correctly recalled, or the relative amount of improvement in mental health
that clients exhibited following their psychotherapy.
1.3.3 INDEPENDENT VARIABLE
Independent variables
reflect the factors that may be said to influence the
dependent variable; they can be conceptualized as
input factors, treatment
