2.2 Summarizing Quantitative Data 45
Cumulative Frequency
10
Audit Time (days)
51520 25 30 35
5
10
15
20
0
FIGURE 2.6 OGIVE FOR THE AUDIT TIME DATA
NOTES AND COMMENTS
1. A bar chart and a histogram are essentially the
same thing; both are graphical presentations of
the data in a frequency distribution. Ahistogram
is just a bar chart with no separation between
bars. For some discrete quantitative data, a sep-
aration between bars is also appropriate. Con-
sider, for example, the number of classes in
which a college student is enrolled. The data
may only assume integer values. Intermediate
values such as 1.5, 2.73, and so on are not pos-
sible. With continuous quantitative data, how-
ever, such as the audit times in Table 2.4, a
separation between bars is not appropriate.
2. The appropriate values for the class limits with
quantitative data depend on the level of accu-
racy of the data. For instance, with the audit time
data of Table 2.4 the limits used were integer
values. If the data were rounded to the nearest
tenth of a day (e.g., 12.3, 14.4, and so on), then
the limits would be stated in tenths of days. For
instance, the first class would be 10.0–14.9. If
the data were recorded to the nearest hundredth
of a day (e.g., 12.34, 14.45, and so on), the lim-
its would be stated in hundredths of days. For
instance, the first class would be 10.00–14.99.
3. An open-ended class requires only a lower class
limit or an upper class limit. For example, in the
audit time data of Table 2.4, suppose two of the
audits had taken 58 and 65 days. Rather than
continue with the classes of width 5 with classes
35–39, 40–44, 45–49, and so on, we could sim-
plify the frequency distribution to show an
open-end class of “35 or more.” This class
would have a frequency of 2. Most often the
open-end class appears at the upper end of the
distribution. Sometimes an open-end class ap-
pears at the lower end of the distribution, and
occasionally such classes appear at both ends.
4. The last entry in a cumulative frequency distri-
bution always equals the total number of obser-
vations. The last entry in a cumulative relative
frequency distribution always equals 1.00 and
the last entry in a cumulative percent frequency
distribution always equals 100.
is used for the 15–19 class, and so on. The “less than or equal to 14” class with a cumula-
tive frequency of 4 is shown on the ogive in Figure 2.6 by the point located at 14.5 on the
horizontal axis and 4 on the vertical axis. The “less than or equal to 19” class with a cumu-
lative frequency of 12 is shown by the point located at 19.5 on the horizontal axis and 12
on the vertical axis. Note that one additional point is plotted at the left end of the ogive. This
point starts the ogive by showing that no data values fall below the 10–14 class. It is plot-
ted at 9.5 on the horizontal axis and 0 on the vertical axis. The plotted points are connected
by straight lines to complete the ogive.
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