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# Feb 13 - PowerPoint PPT Presentation

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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Presentation Transcript

Feb 13, 2009

Prof. Brines

MGH 231

### Making Sense of Charts, Figures, and Graphs

• Rare in research

• Common in media

• Hard to compare wedges (different orientations)

• Can’t show order

• Restrict to nominal variables

• Federal budget, from the website of the War Resisters’ League

• Redrawn

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

• Start vertical above zero

• Exaggerates all differences

• Similar distortion:

• Break vertical axis

Line chart(frequency polygon)

• Common in research

• Can show order

• Appropriate for ordinal and interval variables

• Bar and line charts almost equivalent

• Connect tops

• remove bottoms

• You get a line chart!

• Line eases comparison of groups

• 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)

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

Axis distortion:start (or break) vertical above zero

Axis distortion:Squeeze vertical or stretch horizontal

• NASDAQ stock index, reported by Yahoo!

• Redrawn

• 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