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graph appropriately. We defer a detailed example of creating graphs using the chart
group for the next section.
2.4.2 Some Frequently Used Charts
It is always dangerous to make bold assertions, but it is generally understood that
the mother of all graphs is the Column or Bar chart . They differ only in their
vertical and horizontal orientation, respectively. They easily represent the most often
occurring data situation: some observed numerical variable that is measured in a
single dimension (often time). Consider a simple set of data related to five products
(A–E) and their sales over a two year period of time, measured in millions of dollars.
The first four quarters represent year 1 and the second four year 2. These data are
shown in Table 2.3. Thus, in quarter 1 of the second year, sales for product B results
in sales of $49,000,000.
A quick visual examination of the data in Table 2.3 reveals that the product sales
are relatively similar in magnitude (less than 100), but with differences in quar-
terly increases and decreases within the individual products. For example, product
A varies substantially over the 8 quarters, while product D shows relatively little
variation. Additionally, it appears that when product A shows high sales in early
quarters (1 and 2), product E shows low sales in early quarters—they appear to
be somewhat negatively correlated, although a graph may reveal more conclusive
information. Negative correlation implies that one data series moves in the oppo-
site direction from another; positive correlation suggests that both series move in
the same direction. In later chapters we will discuss statistical correlation in greater
detail.
Let’s experiment with a few chart types to examine the data and tease out insights
related to product A–E sales. The first graph, Exhibit 2.3, displays a simple Column
chart of sales for the 5 product series in each of 8 quarters. The relative magnitude
of the 5 products in a quarter is easily observed, but note that the 5 product series are
difficult to follow through time, despite the color coding. It is difficult to concentrate
solely on a single series, for example Product A, through time.
Table 2.3 Sales data for products A–E
Quarter
A
B
C
D
E
1
98
45
64
21
23
2
58
21
45
23
14
3
23
36
21
31
56
4
43
21
14
30
78
1
89
49
27
35
27
2
52
20
40
40
20
3
24
43
58
37
67
4
34
21
76
40
89
in millions of dollars
 
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