Chapter 11
Displaying Distributions with Graphs
In this chapter
•
StemandLeaf plot
•
Histogram
•
Shapes of Distributions
StemandLeaf plot
The goal with the graphs in this chapter is to look at the distribution for a quantitative
variable. When looking at the graphs presented, it is important to identify if there are
extreme values in the data and the shape of the distribution.
Extreme value
(or
Outlier
) – observations that are separated from the rest of the data set
by some margin
Example
Identify the extreme value in the following data.
14, 15, 17, 21, 60, 23, 25
Answer
The extreme value is 60.
The impact of an extreme value can be great. Suppose we want to estimate the average
income for this class. If John Calipari was in the class, then his income (which is in the
millions) would be an extreme value. That would make the average appear very high
simply because of one observation.
Shape
– the pattern displayed when the graph is created (The most common shapes of
distributions will be introduced at the end of the chapter)
Important characteristics of a stemandleaf
•
Separates data entries into “leading digits” or “stems” and “trailing digits” or “leaves”
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 Fall '10
 Bradley,W
 Sociology, Statistics, Graph Theory, Extreme value

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