Advancing communications measurement and evaluation

Spuriouser and Spuriouser: It’s Raining Correlations

cartoon about correlation vs. causation

The use of Pearson’s r, aka the correlation coefficient, to demonstrate a relationship between two sets of data has long been a standby of public relations measurement and social science research in general. Back in the day, when the calculation of a correlation coefficient required some actual effort at calculation

formula for correlation coefficient

…those who used this statistic had motivation for considering carefully what they were up to (“Think twice, calculate once.”). Not so nowadays, when, in the blink of a cursor, Excel will calculate the correlation coefficient between any two strings of numbers you point it at. Today it’s easy to dredge around in your data and throw as many correlations against the wall as possible, just to see what sticks.

So it’s refreshing to come across Spurious Correlations, a website full of hilarious examples that remind us that that correlations are common and often meaningless. There we find, for instance, that, based on annual data for the U.S., the number of honey producing bee colonies is inversely correlated with the number of juvenile arrests for possession of marijuana, yielding an r = -0.933389:

chart of honey bees vs. marijuana arrests

Also that, also based on annual data for the U.S., the total annual revenue generated by arcades is closely correlated with the number of computer science doctorates awarded, with an r of 0.985065:

chart of arcade revenue vs. computer science doctorates

Spurious Correlations is a humorous warning that correlation does not equal causality. Always take your statistics with a grain of salt.

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Thanks to HFBoards for the cartoon. 

Bill Paarlberg
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Bill Paarlberg

Bill Paarlberg co-founded The Measurement Standard in 2002 and was its editor until July 2017. He also edits The Measurement Advisor newsletter. He is editor of the award-winning "Measuring the Networked Nonprofit" by Beth Kanter and Katie Paine, and editor of two other books on measurement by Katie Paine, "Measure What Matters" and "Measuring Public Relationships." Visit Bill Paarlberg's page on LinkedIn.
Bill Paarlberg
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