Transcript Slide 1

AP Statistics
Stemplots
Describing Distributions
 We can describe the center of a distribution by its
midpoint, the value with roughly half of the values on
each side.
 We can describe spread by giving its smallest and largest
values.
 In describing shape, ask…
 Does the distribution have one or several major peaks
called modes. Those with one mode are unimodal.
 Is the distribution approximately symmetric or is it
skewed?
Describing Distributions
Describing Distributions
Skewed Left
Skewed Right
Symmetric
Interpreting a Histogram
Describe the Histogram
 Shape: roughly symmetric and unimodal
 Center: midpoint around 110
 Spread: about 80 to 150 and no outliers
Penny Ante Histogram
 Describe the Histogram
 for the group data.
 for the class data.
Interpreting a Histogram
A)Describe the shape center
and spread of this distribution.
Are there any outliers?
Skewed to the right, with a center
around 3. The smallest number of
frost days is 0 and the largest number
is 10. There are no gaps or outliers in
this distribution.
B) In what percent of those 65
years did the temperature never
fall below freezing in April?
About 23%
Histogram Tips
 Choose classes that are the same width.
 Use your judgment in choosing classes to display shape.
Too few classes give a sky scraper effect. Too many will
produce a pancake graph.
 Statistical software and graphing calculators will choose
the classes for you. Beware of letting the device choose
your classes.
 Use histograms of percents for comparing several
distributions with different numbers of observations.
Technology Toolbox
Creating a
Histogram using
your Graphing
Calculator.
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