Describing Distributions with Graphs Section 1.1 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 Symmetric Skewed Left Skewed Right

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. Page 21