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How to Describe Data

How to Describe Data. Much of this info is based on a presentation by Marianne W. Zawitz, Bureau of Justice Statistics Link on the course website to: http://www.scs.gmu.edu/~wss/methods/index.html#Graphics Presentation by Dr. Steven Lich-Tyler (Econ professor). Describing Data.

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How to Describe Data

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  1. How to Describe Data

  2. Much of this info is based on • a presentation by Marianne W. Zawitz, Bureau of Justice Statistics • Link on the course website to: http://www.scs.gmu.edu/~wss/methods/index.html#Graphics • Presentation by Dr. Steven Lich-Tyler (Econ professor)

  3. Describing Data • Your goal is to: • convey characteristics about a data sample in a concise and straightforward way • help the reader understand what is going on in your research paper, not confuse or mislead them

  4. Table or Graph? • Use a Graph if: • You want to convey a lot of information in a small space • Illustrate the “big picture” • Use a Table if: • 10 or fewer data points • Exact Numerical Data

  5. A good graph • Presents data clearly • Uses the space efficiently (very little “excess” ink) • Encourages comparisons

  6. Worlds Worst Graph(per Dr. Steven Lich-Tyler) • Discontinuous Axis Misrepresents the scale • Decoration is pointless and confusing • Top portion mirrors the bottom portion – no new information • The percentages are given, making the graph redundant

  7. What Kind of Graph to Use?Continuous Variables • Relative Frequency Histogram • use when distribution of the variable doesn’t follow usual bell shape or other common distribution • Otherwise conventional statistics (mean, s.d., etc.) may be sufficient

  8. What Kind of Graph to Use?Continuous Variables • Line Graph • show trends over time

  9. What Kind of Graph to Use?Continuous Variables • Scatter Plot • show relationship between two variables

  10. What Kind of Graph to Use?Categorical Variables • Bar Graph • Compare across different categories

  11. What Kind of Graph to Use?Categorical Variables • Pie Charts • generally useless • Use a table instead

  12. Graphs: Other Things to Avoid Misleading the Reader with Visual Tricks Poorly Scaled Axes Optical Illusions

  13. Graphs: Other Things to Avoid • Too much non-data ink (gridlines, elaborate graphics, etc)

  14. Tables • Limit Gridlines and Non-Data Ink good bad • Use appropriate number of decimal places good bad

  15. More on Tables • Create a logical visual pattern • Order the content according to how the data will be used or discussed • Place data that are to be compared close to one another • Make patterns and exceptions obvious at a glance • Use notes to explain computed fields

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