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Sociology 220

Sociology 220 Feb 13, 2009 Prof. Brines MGH 231 Making Sense of Charts, Figures, and Graphs Pie chart Rare in research Common in media Hard to compare wedges (different orientations) Can’t show order Restrict to nominal variables An Unhelpful Pie Chart Pie Charts in politics

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Sociology 220

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  1. Sociology 220 Feb 13, 2009 Prof. Brines MGH 231

  2. Making Sense of Charts, Figures, and Graphs

  3. Pie chart • Rare in research • Common in media • Hard to compare wedges (different orientations) • Can’t show order • Restrict to nominal variables

  4. An Unhelpful Pie Chart

  5. Pie Charts in politics • Federal budget, from the website of the War Resisters’ League • Redrawn

  6. Bar chart(column chart) • In research,more common than pie • Can show order • Appropriate for ordinal and interval • (as well as nominal) • Easy to compare vertical distances

  7. Axis distortion • Start vertical above zero • Exaggerates all differences • Similar distortion: • Break vertical axis

  8. Line chart(frequency polygon) • Common in research • Can show order • Appropriate for ordinal and interval variables

  9. Bar vs. line: similarities • Bar and line charts almost equivalent • Start with a bar chart • Connect tops • remove bottoms • You get a line chart!

  10. Bar vs. line: Differences • Line eases comparison of groups

  11. Histograms • Like bar chart, except • Variable typically continuous • Bars touch • usually • Horizontal can represent equal class intervals (“bins”) • Bin shown by center value (e.g. 35.0) • Or by ends of class interval (e.g. 33.75-36.25)

  12. Time series:don’t show distributions,show change over time

  13. Axis distortion:start (or break) vertical above zero

  14. Axis distortion:Squeeze vertical or stretch horizontal

  15. Axis distortion in business • NASDAQ stock index, reported by Yahoo! • Redrawn

  16. Graphics: Good advice • Be skeptical of • Stretched axes (honest aspect is 3:2; Tufte) • Axes that start or break above zero • Graphs that use 3-D • Graphs with many categories/numbers,consider a table instead of a graph

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