Exploring a distribution:
1. Always plot your data: make a graph, usually a histogram or a stemplot.
2. Look for the overall pattern (shape, center, spread) and for striking deviations such as
outliers.
3. Calculate a numerical summary to briefly describe center and spread.
4.
Sometimes the overall pattern of a large number of observations is so regular that we can
describe
it by a smooth curve
.
Density curve: An idealized description of the overall pattern of a distribution that smooths out
the irregularities in the actual data. A density curve has total area 1 underneath it.
A density curve is a curve that
* is always on or above the horizontal axis, and
* has area exactly 1 underneath it.
Outliers, which are deviations from the overall pattern, are not described by the curve.
Of course, no set of real data is exactly described by a density curve. The curve is an idealized
description that is easy to use and accurate enough for practical use.
The median of a density curve is the equalareas point, the point with half the area under the
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 Winter '11
 PattiColling
 Normal Distribution, Standard Deviation, Gary, 68%, 99.7%

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