For a humorous look at what happens if we assume correlation causes causation there's Spurious Correlations: http://www.tylervigen.com/ http://www.tylervigen.co

For a humorous look at what happens if we assume correlation causes causation there's Spurious Correlations: http://www.tylervigen.com/ http://www.tylervigen.com/ My favorite: "Number people who drowned by falling into a swimming-pool correlates with Number of films Nicolas Cage appeared in" With enough variables and noise you'll find things that correlate if you look hard enough. Without experiments where you control one thing and observe the other it's hard to demonstrate causation.