14 Chapter 1 Basic Ideas categories have no natural ordering. Gender is an example of a nominal variable. Figure 1.5 Qualitative Variables illustrates how qualitative variables are divided into nominal and ordinal variables. Ordinal Variables Nominal Variables Figure 1.5 Qualitative variables come in two types: ordinal variables and nominal variables. SUMMARY • Ordinal variables are qualitative variables whose categories have a natural ordering. • Nominal variables are qualitative variables whose categories have no natural ordering. EXAMPLE 1.12 Distinguishing between ordinal and nominal variables Which of the following variables are ordinal and which are nominal? a. State of residence b. Gender c. Letter grade in a statistics class (A, B, C, D, or F) d. Size of soft drink ordered at a fast-food restaurant (small, medium, or large) Solution a. State of residence is nominal. There is no natural ordering to the states. b. Gender is nominal. c. Letter grade in a statistics class is ordinal. The order, from high to low, is A, B, C, D, F. d. Size of soft drink is ordinal. Objective 4 Distinguish between discrete and continuous variables Discrete and Continuous Variables Quantitative variables can be either discrete or continuous. Discrete variables are those whose possible values can be listed. Often, discrete variables result from counting something, so the possible values of the variable are 0, 1, 2, and so forth. Continuous variables can, in principle, take on any value within some interval. For example, height is a continuous variable because someone’s height can be 68, or 68.1, or 68.1452389 inches. The possible values for height are not restricted to a list. Figure 1.6 illustrates how quantitative Quantitative Variables variables are divided into discrete and continuous variables. Discrete Variables Continuous Variables Figure 1.6 Quantitative variables come in two types: discrete variables and continuous variables. SUMMARY • Discrete variables are quantitative variables whose possible values can be listed. The list may be infinite— for example, the list of all whole numbers. • Continuous variables are quantitative variables that can take on any value in some interval. The possible values of a continuous variable are not restricted to any list. EXAMPLE 1.13 Distinguishing between discrete and continuous variables Which of the following variables are discrete and which are continuous? a. The age of a person at his or her last birthday b. The height of a person c. The number of siblings a person has d. The distance a person commutes to work
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