100-Metodos-de-Qualidade-Total

DATA COLLECTION, ANALYSIS AND DISPLAY 159
Method 70
Box and whisker plots
Purpose
To provide a simple way of drawing the basic shape of the distribution of a
set of data.
When to use
In quality monitoring presentation when you want to describe the distribution
of large data and their dispersion in order to carry out exploratory data
analysis.
How to use
The central box contains the central half of the data with the end of the box
marking the quartiles and the central line the median. The whiskers go out
to the extreme values.
With larger data sets, there is a convention that the whisker lines
enclose, say, 97.5 per cent of the data with more extreme values marked
individually. With small data sets, the whiskers end at the largest and
smallest values.
Benefits
Sample method to describe the distribution of data and their variability. In
particular, they help to explore large data in the work of process control.
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Figure 1
A box and whisker plot