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Graphs & Data

Graphs & Data. Data--Types of Variables. Categorical or Quantitative?. Heights of people Level of education Favorite brand of food Distance traveled Zip code. Q C C Q C. Categorical Bar graph Segmented Bar Graph Pie chart. Quantitative Line graph Dotplot Stemplot (Stem & leaf)

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Graphs & Data

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  1. Graphs & Data

  2. Data--Types of Variables

  3. Categorical or Quantitative? • Heights of people • Level of education • Favorite brand of food • Distance traveled • Zip code • Q • C • C • Q • C

  4. Categorical Bar graph Segmented Bar Graph Pie chart Quantitative Line graph Dotplot Stemplot (Stem & leaf) Histogram (Frequency distribution) Boxplot Describing DataThe distribution of a variable tells us what values the variable takes, how often it takes those values, and shows the pattern of variation

  5. What type of graph would display the following data?

  6. Bar, Segmented Bar, & Pie Charts

  7. Line Graphs: showing change over time • Time on the horizontal axis • Connect points to show change over time • Look for an overall pattern or trend (increasing, decreasing, or steady) • Look for striking deviations (big dips or spikes) • Look for seasonal variation –repetitions that occur every year Price of Gasoline

  8. Misleading Graphs • Beware of scaling

  9. Misleading Graphs

  10. CNN’s fixed graph

  11. Same data, but different scales How do the scales effect our impression of the data?

  12. Choosing Scaling • Mayor Marcus is running for a second term against a challenger. Which graph should he send to the local journalist who is reporting on crime rates?

  13. Misleading Graphs • Beware of the pictogram • Bars should have equal width • If the entire area (width and height) is changed, there appears to be a greater increase than really exists

  14. Which graph is better?

  15. What are some problems with this graph?

  16. What’s wrong here?

  17. Ways that Graphs may be Manipulated • Scale and Axis Manipulation (Line, Bar Graphs) • Cropping to focus on desirable information (Especially w/ Line Graphs) • Three dimensional effects (e.g., perspective & “volume”) • Pictorial Embellishments (e.g., “cartoon” effects, leading the readers’ eye) • Mathematical Errors

  18. What do all Graphs need? • Title • Labels • Legend • Accurate scaling • Simplicity so the data is easy to read

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