Evidence-Based Practice for Nurses

it easier to understand, it also results in some loss of information. The grouped
data presented in Table 13-3 indicate that 30% of the subjects were between
20 and 21 years of age; however, there is no way of knowing that most subjects
(five of the six) were 21, and only one subject was 20 years of age.

In addition to frequency distributions, percentage distributions are often
used to present descriptive statistics. A percentage distribution is calculated by
dividing the frequency of an event by the total number of events. For example,
in Table 13-3 the three 18-year-old subjects in the study represent 15% of the
total number of subjects reported. Providing information about percentages
is another way to group data to make results more comprehensible and allow
for easier comparisons with other studies.

After data are tallied and a frequency distribution is determined, data may
be converted to graphic form. Graphs provide a visual representation of data
and often make it easier to discern trends. The most common types of graphs
are line charts, bar graphs, pie charts, histograms, and scattergrams (or scat-
terplots). Figure 13-1 depicts two different ways to present the age data from
Table 13-3.

Raw Data

18 18 18 19 19 19 20 21 21 21 21 21 22 22 22 23 23 25 27 28

Ungrouped Data Grouped Data

Age Tally Frequency Percentage Age Tally Frequency Percentage

18 ||| 3 15 18–19 |||| | 6 30

19 ||| 3 15 20–21 |||| | 6 30

20 | 1 5 22–23 |||| 5 25

21 |||| 5 25 24–25 | 1 5

22 ||| 3 15 > 25 || 2 10

23 || 2 10 Total 20 100

25 | 1 5

27 | 1 5

28 | 1 5

Total 20 200

TABLE 13-3

Example of Frequency and Percentage Distributions

of Ages

KEY TERM

percentage

distributions:

Descriptive

statistics used

to group data to

make results more

comprehensible;

calculated by

dividing the

frequency of an

event by the total

number of events

13.2 Using Frequencies to Describe Samples 335