Data have been obtained on the lives of batteries of a particular type in an industrial application. Table 4.1 shows the lives of 36 batteries recorded to the nearest tenth of a year.
Table 4.1: Battery Lives, years
4.1
5.2
2.8
4.9
5.6
4.0
4.3
5.4
4.5
6.1
3.7
2.3
3.9
3.2
5.0
4.8
4.6
5.5
1.8
5.1
4.2
6.3
3.3
5.8
4.4
3.0
4.7
For these data we choose “stems” which are the main magnitudes. In this case the digit before the decimal point is a reasonable choice: 1,2,3,4,5,6. Now we go through the data and put each “leaf,” in this case the digit after the decimal point, on its corresponding stem. The decimal point is not usually shown. The result can be seen in Table 4.2. The number of stems on each leaf can be counted and shown under the heading of Frequency.
Table 4.2: Stem-and-Leaf Display
Stem
Leaf
Frequency
1
8
2
8 3
3
7 9 2 7 3 0
6
4
1 9 0 1 3 5 5 9 3 8 6 2 4 8 3 7
16
5
2 6 4 6 0 5 1 8 1
9
1 3
relative numbers. We can see whether or not the distribution is approximately symmetrical, and we may get a preliminary indication of whether any particular theoretical distribution may fit the data. We will see some theoretical distributions later in this book, and we will find that some of the distributions we encounter in this chapter can be represented well by theoretical distributions.
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