The Normal Distribution
The normal distributions are a very important
class
of statistical distributions. All normal distributions are
symmetric and have bellshaped density curves with a single peak.
To speak specifically of any normal distribution, two quantities have to be specified: the mean
, where the
peak of the density occurs, and the standard deviation
, which indicates the spread or girth of the bell curve.
(The greek symbol
is pronounced
mu
and the greek symbol
is pronounced
sig
ma
.)
Different values of
and
yield different normal density curves and hence different normal distributions.
Try the applet below for example. You should be able to change the mean
and the standard deviation
using the sliders and see the density change.
Object 1
The normal density can be actually specified by means of an equation. The height of the density at any value
x
is given by
Although there are many normal curves, they all share an important property that allows us to treat them in a
uniform fashion.
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 Winter '09
 scotty
 Normal Distribution, Standard Deviation, 5%, 2.5%, 5 inches

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