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Lecture 3: Displaying Data
Chapter 2, Whitlock and Schulter, 2nd Ed
Key questions:
What makes a good graph?
What makes a bad graph?
Types of graphs for types of different data
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Basics Rules of plotting data
1) Show the raw data if possible
2) Show distributional info if possible
3) ALWAYS Include error bars around means
4) ALWAYS Include error bars around means
5) Make patterns in the data easy to see
6) Represent magnitude honestly
7) Draw graphical elements clearly
8) Include a legend and label things clearly
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Plotting Rule #1: Show the raw data
Compare the information content of these two graphs
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Plotting Rule #1: Show the Data
Multiple datasets can result in the exact same barplot & errorbars
Bar plots – even with error bars – therefore reveals very little about the data
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Plotting Rule #2: Show distributional information
Distributional info can be displayed by plotting the raw data or by using boxplots
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Plotting Rule #3 & 4: Alwys use error bars for means
Means MUST always have an estimate of uncertainty around them
The range doesn’t count!
Typically use “standard error” OR “confidence interval”
Rarely use “standard deviaiton”
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Plotting Rule #5: Make Patterns Easy to See
Keep it as simple as possible
Add labels, annotations etc.
Use both color AND pattern/shape to distinguish groups
Avoid 3D
Use color-blind friendly palettes
Don’t use most of the fancy stuff in Excel!
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Plotting Rule #5: Make Patterns Easy to See example
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Plotting Rule #6: Represent Magnitudes Honestly
This plot emphasizes a certain aspect of data
Some critics think this is desceptive
What else is missing?
Original Paper: aeaweb.org/articles?id=10.1257/jep.25.1.159 Oreopoulos & Salvanes. 2011. Priceless: The Nonpecuniary Benefits of Schooling. Jrn Econ Persp.
Critiques: econlog.econlib.org/archives/2011/07/job_satisfactio.html scienceblogs.com/principles/2011/07/10/great-moments-in-deceptive-gra/ See statisticshowto.com/misleading-graphs/ for some more interesting examples
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Histograms of discrete data
Number of extinct birds from each Hawaiian island 
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Histograms of continous data
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Graphing association between categorical variables
aka, Turning a contingency table into a graph
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Misc. References
Websites www.biostat.wisc.edu/~kbroman/topten_worstgraphs/ www.americanscientist.org/issues/pub/population-growth-technology-and-tricky-graphs
Papers Wainer. 1984. How to Display Data Badly. Am. Statistician.