Statistics for the Behavioral Sciences by Frederick J. Gravetter, Larry B. Wallnau ISBN 10: 1305504917 ISBN 13: 9781305504912

SECTION 1.3 | Variables and Measurement 19
behaviors that can be observed and measured. For example, your intelligence is measured
and defined by your performance on an IQ test, or hunger can be measured and defined by
the number of hours since last eating.
DEFINITION
Constructs are internal attributes or characteristics that cannot be directly
observed but are useful for describing and explaining behavior.
An operational definition identifies a measurement procedure (a set of operations)
for measuring an external behavior and uses the resulting measurements as
a definition and a measurement of a hypothetical construct. Note that an operational
definition has two components. First, it describes a set of operations for
measuring a construct. Second, it defines the construct in terms of the resulting
measurements.
■ Discrete and Continuous Variables
The variables in a study can be characterized by the type of values that can be assigned to
them. A discrete variable consists of separate, indivisible categories. For this type of variable,
there are no intermediate values between two adjacent categories. Consider the values
displayed when dice are rolled. Between neighboring values—for example, seven dots and
eight dots—no other values can ever be observed.
DEFINITION
A discrete variable consists of separate, indivisible categories. No values can exist
between two neighboring categories.
Discrete variables are commonly restricted to whole, countable numbers—for
example, the number of children in a family or the number of students attending class.
If you observe class attendance from day to day, you may count 18 students one day
and 19 students the next day. However, it is impossible ever to observe a value between
18 and 19. A discrete variable may also consist of observations that differ qualitatively.
For example, people can be classified by gender (male or female), by occupation
(nurse, teacher, lawyer, etc.), and college students can by classified by academic major
(art, biology, chemistry, etc.). In each case, the variable is discrete because it consists
of separate, indivisible categories.
On the other hand, many variables are not discrete. Variables such as time, height, and
weight are not limited to a fixed set of separate, indivisible categories. You can measure
time, for example, in hours, minutes, seconds, or fractions of seconds. These variables
are called continuous because they can be divided into an infinite number of fractional
parts.
DEFINITION
For a continuous variable, there are an infinite number of possible values that fall
between any two observed values. A continuous variable is divisible into an infinite
number of fractional parts.
Suppose, for example, that a researcher is measuring weights for a group of individuals
participating in a diet study. Because weight is a continuous variable, it can be pictured as
a continuous line (Figure 1.7). Note that there are an infinite number of possible points on