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In addition to classifying variables by their scale of measurement, there is another way that researchers classify variables. This second classification system is not as closely tied to statistical analyses as are the scales of measurement, but as you will observe these terms used in research, I want you to be aware of them.

A discrete variable typically takes a whole-number value. For example, the number of children in a family is a discrete variable because only whole numbers are possible. A change in the value of a discrete value occurs one whole number at a time. If a family with three children has another child, it now has four children. No single value can occur between three and four in this example. Table 2.4 contains some examples of discrete variables in Terrell et al.’s (2008) research. We see that the variables of sex, class standing, and ethnicity are discrete variables. For each one, a respondent takes on one value or category. Most of the time, discrete variables will be measured on a nominal or an ordinal scale.

A continuous variable is one whose measurement can take on fractional values. For example, time is a continuous variable. The passage of time may be broken into an infinite number of units. When running a 40-yard dash, one person may run it in five seconds and another person may run it in six seconds. A third person could run that distance between those two times, for instance, in 5.4 seconds. The term “continuous” means that numbers continue between the whole numbers. In Terrell et al.’s (2008) research, GPA, height, and weight are continuous variables. In addition, the three personality measures are also continuous variables. At first glance, this may seem confusing. Let’s examine the tendency to act aggressively by examining some sample items that appear at the bottom of Table 2.4. Respondents used a 1–5 response range to indicate how much each statement describes them. If we average the responses across all items on this survey, then indeed, we can obtain fractional values, which is why this is a continuous variable. Most of the time, continuous variables will be quantified by using a scale (interval or ratio) measurement.

Table 2.4 Examples of Discrete and Continuous Variables in Terrell et al.’s (2008) Research

Discrete variable: variable that can have only a whole number value.

Continuous variable: variable that can have a fractional value.