Rutgers University - Center for Vector Biology

Graphing Data: Have I Got Graphing Data: Have I Got a Story to Tell…a Story to Tell…

Lisa Reed, Ph.DLisa Reed, Ph.DCenter for Vector BiologyCenter for Vector Biology

Rutgers UniversityRutgers University26 April 201226 April 2012

Rutgers University - Center for Vector Biology

For Today

• Graph Importance• Examples, both good and

bad• What are good graphs and

good graph rules• How do you make a good

graph– Excel graph designs– Others

• How to get them from Excel to Word

Rutgers University - Center for Vector Biology

“The greatest value of a picture is when it forces

us to notice what we never expected to see.”

Tukey, 1977, Exploratory Data Analysis

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Why Are Graphs Important?

• Can give information quickly

• Can highlight the point you want to make

• Can direct towards statistical tools

• But can give misinformation if not careful

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Napoleon’s March to and From Moscow by Minard

• Shows number of troops in geography and travel• Shows temperature and time• Gives an understanding for Napoleon’s failure

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Snow’s Cholera Well

• Identifies cholera deaths (in red)

• Identifies wells (in blue)

• Implicates cholera as a water-borne disease

• Clearly indicates which well should be shut down.

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Simple Statistical Graphs

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Not so good.

From junkcharts.typepad.com

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What Makes A Good Graph?

• Simple and efficient: Presents one basic conclusion.• Clear and Unambiguous: You understand what is being

presented.• Not Misleading: You don’t come to a wrong conclusion.• Meaningful: You come to a correct and relevant

conclusion.

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Achieving Good Graphics

• Use Titles – What are you trying to show?• Use Axis Labels – Tell what you are graphing.• Use Units of Measurements – Tell what you are

graphing.• Use legends.• Use Series coloration/fills – but be careful for those

who are colorblind.• Keep scaling appropriate.• Write out equations when appropriate.• Use error bars when available.

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Use Titles, Labels, Units of Measure, Legends

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Fills & Colorblindness

• Patterns (but must load patterns if using Excel 2007)

• Labels• 1 Color and Brightness• Grayscale

http://www.colblindor.com/2007/06/02/how-to-color-charts-respecting-color-blindness/

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You can run a colorblind checker…

• http://www.vischeck.com/vischeck/vischeckImage.php

• Browse to your image and run the checker.

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Scale

• Generally begin at zero.

• But look at data.• If more than 1 graph

on a page, try to use same scale.

• If you cannot use one scale, make it obvious that the scales differ.– Different colors– Different gridlines

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Equations and Error Bars

• Both elements give added information.

• But need specific information– Regression lines need

the equation AND the R2

– Error bars need the type.

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Making Graphs in Excel

• Highlight Data• Choose Graph Style…• Voila!

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Editing Graphs in Excel

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Changing Chart Types

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Switch Row/Column

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Adding Titles, Labels and Legends

Hold Down the Alt key and type from the keypad numbers:Alt 241 = ±Alt 248 = °

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No Fills Available for versions 2007!

• But, download add-in– http://officeblogs.ne

t/excel/PatternUI.zip

• Unzip file (and remember where it is)

• Go to Window Flower, Excel Options, Add-in, Go and click Patternui.

• Click on series in graph, go to Chart Tools, Format, Patterns and select which one you want.

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Scale

• Generally begin at zero.

• But look at data.• If more than 1 graph

on a page, try to use same scale.

• If you cannot use one scale, make it obvious that the scales differ.– Different colors– Different gridlines

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Equations

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The Agony and the Ecstasy of Error Bars

• You have a set of data.• You do a pivot table to summarize average and SD.• You plot average with the intention of doing SD as

error bars:

• You have a set of data.• You do a pivot table to

summarize average and SD.

• You copy and paste values, THEN create your graph:

X

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Achieving Good Graphics

• Use Titles • Use Axis Labels • Use Units of Measurements• Use legends.• Use series coloration/fills.• Keep scaling appropriate.• Write out equations when appropriate.• Use error bars when available.

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Why this Class?

• Resistance Classes

• Graphs

• Simple Statistics

• Probit Analysis

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Suggested References

• The Visual Display of Quantitative Information – Edward Tufte, 1983

• How to Lie with Statistics – Darrell Huff, 1994