### Math 225 Course Notes

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### Chapter 2

#### Contents

Data from a single variable is best summarized by a graph.
You will learn how to make and interpret
histograms
and stem-and-leaf displays.
Graphs also help to identify unusual observations or
outliers.
The distribution of each variable is described by summarizing
its center, spread, and shape.
The two most important numerical summaries of center are
the mean
and the median.
The most important numerical summary of spread
is the standard deviation.
The variance
is simply the square of the standard deviation.
The shape of a graph may frequently be described as being
symmetric
or skewed
to the left or right.
It may be bell-shaped, or perhaps bimodal.

Last modified: Jan 15, 1996

Bret Larget,
larget@mathcs.duq.edu