Download - What’s So Funny About Correlation?
Cartoon from xkcd.com
What’s So Funny About Correlation?
What is Correlation?
• When two things go together:
• cookies & milk
• macaroni & cheese
• peanut butter & jelly
What is Statistical Correlation?
• A mutual relationship between two variable quantities.
• Correlation coefficients measure how closely related the two variables are.
Correlation Coefficient Strength
1 Perfect Positive
0.7 to 0.9 Strong Positive
0.4 to 0.6 Moderate Positive
0.1 to 0.3 Weak Positive
0 No Correlation
-0.1 to -0.3 Weak Negative
-0.4 to -0.6 Moderate Negative
-0.7 to -0.9 Strong Negative
-1 Perfect Negative
Does the amount of uranium stored at nuclear plants correlate with the amount of
power they generate?
Does the amount of uranium stored at nuclear plants correlate with the amount of
power they generate?Year Uranium Power
1984 160.2 327.6
1985 153.2 383.7
1986 144.1 414
1987 137.8 455.3
1988 125.5 527
1989 115.8 529.4
1990 102.7 576.9
1991 98 612.6
1992 92.1 618.8
1993 81.2 610.3
1994 65.4 640.4
1995 58.7 673.4
1996 66.1 674.7
1997 65.9 628.6
1998 65.8 673.7
1999 58.3 728.3
2000 54.8 753.9
2001 55.6 768.8
2002 53.5 780.1
2003 45.6 763.7
2004 57.7 788.5
2005 64.7 782
2006 77.5 787.2
2007 81.2 806.4
2008 81.9 806.2
Graph from www.tylervigen.com
Does the amount of uranium stored at nuclear plants correlate with the amount of
power they generate?
Does the amount of uranium stored at nuclear plants correlate with the amount of power they generate?
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Uranium Stored vs Power Generated
Uranium Stored
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Does the amount of uranium stored at nuclear plants correlate with the amount of power they generate?
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Uranium Stored vs Power Generated
Uranium Stored
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Does the amount of uranium stored at nuclear plants correlate with the amount of power they generate?
Does the amount of uranium stored at nuclear plants correlate with the amount of power they generate?
-0.89905
Why might the amount of uranium stored at nuclear plants correlate with the amount of power
they generate?
What is Causation?
What is Causation?• The action of causing something;
the relationship between cause and effect.
• Smoking causes cancer
• Sugar causes cavities
• Gravity causes objects to fall
How does per capita consumption of chicken correlate with crude oil imports?
Graph from www.tylervigen.com
How does per capita consumption of chicken correlate with crude oil imports?
Chicken data from USDA. Oil data from Dept. of Energy.
How does per capita consumption of chicken correlate with crude oil imports?
Year Per capita chicken consumption (lbs.)
Total crude oil imports (millions of barrels)
2000 54.2 3311
2001 54 3405
2002 56.8 3336
2003 57.5 3521
2004 59.3 3674
2005 60.5 3670
2006 60.9 3685
2007 59.9 3656
2008 58.7 3571
2009 56 3307
How does per capita consumption of chicken correlate with crude oil imports?
0.9
How does per capita consumption of chicken correlate with crude oil imports?
53 54 55 56 57 58 59 60 61 623100
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3300
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Chicken Consumption vs. Crude Oil Imports
Chicken
Oil
How does per capita consumption of chicken correlate with crude oil imports?
53 54 55 56 57 58 59 60 61 623100
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Chicken Consumption vs. Crude Oil Imports
Chicken
Oil
Does eating more chicken cause crude oil imports to increase?
?
Correlation and Causation• Correlation is a measure of how well data fit the relationship.
• A correlated relationship between two quantitative variables is not the same as a causal relationship.
• The determination that one thing causes another requires a controlled randomized experiment.
• "Correlation is not causation, but it sure is a hint.“- Edward Tufte, American Statistician
Cartoon from xkcd.com
What’s So Funny About Correlation?