Variables
Prerequisites
none
Learning Objectives
 Define and distinguish between independent and dependent variables
 Define and distinguish between discrete and continuous variables
 Define and distinguish between qualitative and quantitative variables
Independent and dependent
variables
Variables are properties or characteristics of
some event, object, or person that can take on different values
or amounts (as opposed to constants such as π
which do not vary). When conducting research, experimenters often
manipulate variables. For example, an experimenter might compare
the effectiveness of four types of antidepressants. In this case,
the variable is "type of antidepressant." When a variable
is manipulated by an experimenter, it is called an independent
variable. The experiment seeks to determine the effect of
the independent variable on relief from depression. In this example,
relief from depression is called a dependent
variable. In general the independent variable is manipulated
by the experimenter and its effects on the dependent variable
are measured.
Qualitative and
Quantitative Variables
An important distinction between variables
is between qualitative
variables and quantitative
variables. Qualitative variable are those that express a
qualitative attribute such as hair color, eye color, religion,
favorite movie, gender, and so on. The values of a qualitative
variable do not imply a numerical ordering. Values of the variable “religion”
differ qualitatively; no ordering of religions is implied. Qualitative
variables are sometimes referred to as categorical
variables. Values on qualitative variables do not imply
order, they are simply categories. Quantitative variables
are those variables that are measured in terms of numbers.
Some examples of quantitative variables are height, weight,
and shoe size.
Discrete and Continuous
Variables
Variables such as number of children in a household
are called discrete
variables since the possible scores are discrete points on
the scale. For example, a household could have three children
or six children, but not 4.53 children. Other variables such as
"time to respond to a question" are continuous
variables since the scale is continuous and not made up of
discrete steps. The response time could be 1.64 seconds, or it
could be 1.64237123922121 seconds. Of course, the practicalities
of measurement preclude most measured variables from being truly
continuous.
