2 Descriptive Methods for Continuous Data
A class of measurements or a characteristic on which individual observations
or measurements are made is called avariable; examples include weight, height,
and blood pressure, among others. Suppose that we have a set of numerical
values for a variable:
- If each element of this set may lie only at a few isolated points, we have a
discretedata set. Examples are race, gender, counts of events, or some
sort of artificial grading. - If each element of this set may theoretically lie anywhere on the numeri-
cal scale, we have acontinuousdata set. Examples are blood pressure,
cholesterol level, or time to a certain event such as death.
In Chapter 1 we dealt with the summarization and description of discrete
data; in this chapter the emphasis is on continuous measurements.
2.1 TABULAR AND GRAPHICAL METHODS
There are various ways of organizing and presenting data; simple tables and
graphs, however, are still very e¤ective methods. They are designed to help the
reader obtain an intuitive feeling for the data at a glance.
2.1.1 One-Way Scatter Plots
One-way scatter plots are the simplest type of graph that can be used to sum-
marize a set of continuous observations. A one-way scatter plot uses a single
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