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Frequency
2.2 Visualizing Quantitative Data
To make an assessment of how efficient the technical support department is in helping customers
solve software issues, management keeps track of the length of each phone call taking place over
the day. They find the following:
Length of Call (min.)
1 2 13 4 12
4 10 6 6 9
4 3 4 0 12
6 4 4 13 15
0 4 10 4 10
7 2 10 8 4
7 0 4 4 4
Since this data is quantitative, the discussed visual displays are not appropriate. However,
management still would like to visualize the 35 observations.
One quick, by-hand technique to visualize how the times appear would be a dot plot, or a simple
number line, with any repeats stacked above others. Given the presence of great technology, we
will use Excel to create a histogram, which is a graph similar to a bar graph (can be either
frequency or relative frequency). The difference is that, instead of having nominal categories on
the horizontal axis, we will create numerical categories. For example, we could simply create
tick marks for each observation value present in the table and to then display the number of time
it appears. Often, with small amounts of data, the graph may appear spread out. In this case, we
might decide to create a bar representing, say, all calls that fall between 0 and 3 minutes. Let‟s
demonstrate both:
14
12
10
Call Times
8
6
4
2
0
0 1 2 3 4 6 7 8 9 10 12 13 15
Length (min.)
Statistics for Decision-Making in Business © Milos Podmanik Page 43