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A valid measure?. Statistical graphs: The good, the bad and the ugly.

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Presentation on theme: "A valid measure?. Statistical graphs: The good, the bad and the ugly."— Presentation transcript:

1 A valid measure?

2 Statistical graphs: The good, the bad and the ugly

3 Challenger disaster On Jan. 28, 1986, the space shuttle Challenger exploded after blastoff, killing 7 astronauts Cause of the explosion was failure of rubber O-rings sealing two sections of the rockets. The O-rings failed due to the low temperature at the time of the launch which made the O-rings brittle. The day before, engineers had recommended postponing the launch because of the low temperature forecast.

4 This is the graph that NASA staff looked at. It shows data from past flights where there had been O-ring failures. (Report of the Presidential Commission on the Space Shuttle Challenger Accident)

5 O-ring damage index Temperature and O-Ring Damage SRM 15 SRM 22 26 - 29 deg. range of forecasted temperatures O-ring damage index

6 The Good...

7 John Snow’s map of 1854 London cholera epidemic

8 Mortality in the Crimean War Florence Nightingale, nurse and statistician Chief nurse in Crimean War (1854-56) Graph produced after seeing sanitary conditions in the Crimea. Shows far more deaths from non- battle causes than battle- related causes. “To understand God’s purpose we must study statistics, for these are the measure of His purpose.”

9 Trellis plot of barley yields from an agricultural field experiment at six sites in Minnesota. Ten varieties of barley were grown in each of two years.

10 “The best graphic ever produced”– Edward Tufte Napoleon’s 1815 March on Moscow

11 Gun death rate: 36 richest countries

12 Interactive Graphs How Different Groups Spend Their Day CO2 Emissions Since 1820

13 What makes good graphs “Excellence in statistical graphics consists of complex ideas communicated with clarity, precision, and efficiency.” – Edward Tufte Good graphical displays should –Show the data –Avoid distortion –Make large datasets coherent –Serve a clear purpose

14 The Bad...


16 Chartjunk



19 Chartjunk “Lurking behind chartjunk is contempt both for information and for the audience. Clarity and simplicity are the complete opposite of simple-mindedness. Data- thin, forgetful displays move viewers toward ignorance and passivity.” -- Edward Tufte

20 Required fuel economy standards set by the Department of Transportation—from 18 to 27.5 mpg, an increase of 53% The increase shown in the graph is 783%!


22 Violation of Area Principle: The area occupied by a part of the graph should correspond to the magnitude of the value it represents.


24 2-D Pie Chart 3-D Pie, Exploded 3-D Column Bar Simple 2-D Bar The problem with pie charts



27 Source: The Economist How to compare the years on the left? Adding a dimension adds confusion



30 Components of a good graph Label clearly Use consistent scales Legends should tell what variables are plotted, their units, and the source of the data Make it simple, avoid clutter A graph is not a creative piece of art. Focus on the data

31 And The Ugly

32 "This may well be the worst graphic ever to find its way into print." -- Edward Tufte


34 Or is this graph the worst? How many things can you find wrong?

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