CHAPTER 4
FREQUENCY TABLES AND THEIR
GRAPHS
Usually, we can obtain only a rather vague impression from looking at a set of data,
especially with a large data set. The complexity that the mind can grasp is limited,
and some form of summarizing the data becomes necessary. In this chapter and
in Chapter 5, commonly used ways of depicting data are considered. The general
purpose of Chapters 4 and 5 is to show how data can be described in a form that alerts
the reader to the important features of the data set. We regard such descriptions as
a first step in analyzing data; frequently, it is the only step that needs to be taken.
With small data sets it can be done by hand, but with larger sets statistical computer
programs should be used.
In this chapter, a straightforward way of showing the distribution of the data is
given. Additional methods are given in the next chapter. The methods given here are
used mainly for what are called continuous variables. Continuous variables are not
restricted to a particular value and can be measured to different levels of accuracy.
For example, length could be expressed as 10 cm, 10.1 cm, or 10.13 cm. In contrast,
discrete variables can only take on integer values. An example would be the number
of children in a family. For additional information on classifying variables, see
Section 5.4.3.Basic Statistics: A Primer for the Biomedical Sciences, Fourth Edition.
By Olive Jean Dunn and Virginia A. Clark
Copyright @ 2009 John Wiley & Sons, Inc.35