Displaying Distributions – Qualitative Variables Lecture 12 Sections – Wed, Feb 8, 2006

Pie Charts Pie chart – A graph in which Pie chart – A graph in which Each pie slice represents one category. Each pie slice represents one category. The width (central angle) of the pie slice is proportional to the number of members in the category. The width (central angle) of the pie slice is proportional to the number of members in the category.

Pie Charts The pie chart shows (as a percentage or a count) what part each category is of the whole. The pie chart shows (as a percentage or a count) what part each category is of the whole. Use the percentage associated with the category to compute the central angle of the pie slice. Use the percentage associated with the category to compute the central angle of the pie slice. E.g., 25% of 360  = 90 . E.g., 25% of 360  = 90 . A pie chart facilitates the comparison of one category to the whole. A pie chart facilitates the comparison of one category to the whole.

Example The enrollment for this course consists of The enrollment for this course consists of 16 freshmen 16 freshmen 2 sophomores 2 sophomores 1 junior 1 junior 2 seniors 2 seniors Draw a pie chart of these data. Draw a pie chart of these data. Is a pie chart an appropriate display of these data? Is a pie chart an appropriate display of these data? What does it tell us? What does it tell us?

Bar Graphs Bar graph – A graph in which Bar graph – A graph in which Each bar represents one category. Each bar represents one category. The height (or length) of a bar is proportional to the number of members in the category. The height (or length) of a bar is proportional to the number of members in the category.

Bar Graphs The bar displays the relative size of the category, as measured on the vertical scale (as a percentage or a count). The bar displays the relative size of the category, as measured on the vertical scale (as a percentage or a count). A bar graph facilitates the comparison of one category to another. A bar graph facilitates the comparison of one category to another.

Example The enrollment for this course consists of The enrollment for this course consists of 16 freshmen 16 freshmen 2 sophomores 2 sophomores 1 junior 1 junior 2 seniors 2 seniors Draw a bar graph of these data. Draw a bar graph of these data. Is a bar graph an appropriate display of these data? Is a bar graph an appropriate display of these data? What does it tell us? What does it tell us?

Example Example: HSC Fact book. Example: HSC Fact book.HSC Fact bookHSC Fact book Excel spreadsheet: HSC Facts.xls. Excel spreadsheet: HSC Facts.xls.HSC Facts.xlsHSC Facts.xls

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