Displaying Distributions – Qualitative Variables Lecture 14 Sections – Fri, Sep 14, 2007

Pie Charts Pie chart. Use the percentage associated with the category to compute the central angle of the pie slice.  E.g., 25% of 360  = 90 . A pie chart facilitates the comparison of one category to the whole.

Case Study 8 Meet Pie-Chart Pam.Pie-Chart Pam  Who gets pulled over. Who gets pulled over What does the pie chart tell us? Is a pie chart an appropriate display of these data?

Who Gets Pulled Over How does the distribution by race of those pulled over compare to the distribution in the general population? PopulationPulled Over White73%65% Black20%24% Hispanic6%7%

Who Gets Pulled Over The sample consisted of 520,079 cases. If we compute the p-value, we get p-value < Is that significant?

Who Gets Pulled Over An interesting question raised by the superintendent of the Virginia State Police: “Do we know, at any given hour, what the demographics of I-95 in Richmond may be?” What kind of bias (other than racial profiling) may be in play here?

Case Study 9 Who gets bitten. Who gets bitten

Bar Graphs Bar graph. A bar graph facilitates the comparison of one category to another.

Example Pie-Chart Pam also does bar graphs. Pie-Chart Pam  Who get pulled over. Who get pulled over What does it tell us? Is a bar graph an appropriate display of these data?

Pie Chart Examples Where Your Income Tax Money Really Goes Where Your Income Tax Money Really Goes Major Religions of the World Ranked by Number of Adherents Major Religions of the World Ranked by Number of Adherents Warning against using piecharts