This frequency table is shown in Table 2–1. The number of observations in each
class is called the
class frequency.
So the class frequency for domestic vehicles
sold is 50.
FREQUENCY TABLE
A grouping of qualitative data into mutually exclusive classes
showing the number of observations in each class.
TABLE 2–1
Frequency Table for Vehicles Sold at Whitner Autoplex Last Month
Car Type
Number of Cars
Domestic
50
Foreign
30
Relative Class Frequencies
You can convert class frequencies to
relative class frequencies
to show the frac-
tion of the total number of observations in each class. So, a relative frequency cap-
tures the relationship between a class total and the total number of observations.
In the vehicle sales example, we may want to know the percent of total cars sold
that were domestic or foreign.
To convert a frequency distribution to a
relative
frequency distribution, each of
the class frequencies is divided by the total number of observations. For example,
0.625, found by 50 divided by 80, is the fraction of domestic vehicles sold last
month. The relative frequency distribution is shown in Table 2–2.

Graphic Presentation of Qualitative Data
The most common device to present a qualitative variable in graphic form is a
bar
chart.
In most cases the horizontal axis shows the variable of interest and the verti-
cal axis the amount, number, or fraction of each of the possible outcomes. A distin-
guishing characteristic of a bar chart is the distance or gap between the bars. That
is, because the variable of interest is qualitative, the bars are not adjacent to each
other. Thus, a bar chart graphically describes a frequency table using a series of uni-
formly wide rectangles, where the height of each rectangle is the class frequency.
Describing Data: Frequency Tables, Frequency Distributions, and Graphic Presentation
23
BAR CHART
A graph in which the classes are reported on the horizontal axis
and the class frequencies on the vertical axis. The class frequencies are
proportional to the heights of the bars.
Foreign
C
ar Type
(Variable of intere
s
t)
Number
S
old
(
C
la
ss
frequency)
Dome
s
tic
0
10
20
30
40
50
6
0
CHART 2–1
Vehicle Sold by Type Last Month at Whitner Autoplex
TABLE 2–2
Relative Frequency Table of Vehicles Sold by Type at Whitner Autoplex Last Month
Vehicle Type
Number Sold
Relative Frequency
Domestic
50
0.625
Foreign
30
0.375
Total
80
1.000
We use the Whitner Autoplex data as an example (Chart 2–1). The variable of inter-
est is the vehicle type and the number of each type sold is the class frequency. We
scale the vehicle type (domestic or foreign) on the horizontal axis and the number
of each item on the vertical axis. The height of the bars, or rectangles, corresponds
to the number of vehicles of each type sold. So for the number of foreign vehicles
sold the height of the bar is 30. The order of foreign or domestic on the
X-
axis does
not matter because the values of car type are qualitative.

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- Spring '11
- Leany
- Frequency, The American, The Federalist Papers, Frequency distribution, Histogram, Summary statistics, Whitner Autoplex