“Extrapolating patterns beyond their natural range can lead to false conclusions” PhD statistician Christine Anderson-Cook in the October issue of Quality Progress. * That should be obvious to everyone. Unfortunately, though, one naturally “eye fits” the final leg of every graph straight out into the beyond of the X axis, thus overlooking the possibility of an imminent bend such as the one shown here by Gapminder. A classic case of this occurred a decade ago when a consensus of forecasters predicted that all of the world economies would experience continued expansion in 2009—none foreseeing the Great Recession. **
“Avoid Linear extrapolation … The turkey’s first 1000 days are a seemingly unending succession of gradually improving circumstances confirmed by daily experience. What happens on Day 1001? Thanksgiving.”
-John E. Sener (Source: Consortium for the Advancement of Undergraduate Statistics Education)
Be careful out there!
* “Straight Line or Not?” p45.
** Financial Times, “An astonishing record – of complete failure”, Tim Harford, May 30, 2014