100-Metodos-de-Qualidade-Total

DATA COLLECTION, ANALYSIS AND DISPLAY 219
Method 95
Stem and leaf diagram
Purpose
To present raw data and to show their distribution visually.
When to use
As a tool in exploratory data analysis such as histograms. It is useful for
illustrating large amounts of data.
How to use
Round numerical data to the number of tens by trimming off the last digits.
In Figure 1 the ascending order of the data is 3, 5,6, 7, 7, 8, 8, 9 . .. 33, 35.
The last digit of each observation is called a leaf and the other digits form a
stem. For an observation of 35, the leaf is 5 and the stem is 3.
Benefits
1 A stem and leaf diagram sideways provides a histogram of the data with
numerical values.
2 The method can be modified to suit different data.
3 Ouartiles, i.e. 01 , O2 etc. can be read directly.
4 The diagram gives a useful five-number summary, i.e. lower quartile,
median, upper quartile, the smallest and the target value.
Tens
Units
0 3
0 56777889
1 01 1 2233344
1 5556677788899
2 01 1233
2 5578899
3 0123
3 5
Stem
Leaf
Total
1
8
10-- 01
13-- 02
6" 03
7
4
1
50
Figure 1
Stem and leaf diagram