Correlation does not mean causation

A variety of images showing that correlation does not imply causation.

A plot showing the relationship between the number of Nobel prizes earned in each country, and chocolate consumption. Both data are adjusted by the population of each country (an indirect source of this graph here).

Phenomena like the shown in the image above usually come from the fact that both variables involved correlate highly with a third (not shown) variable. Many times this third variable is population (source: xkcd)

The fact that a linear association might be easily confounded with a causal relationship may be the reason of the mith that storks deliver babies. This article shows the strong correlation between stork population and human birth rate.

Conclusion, keep in mind that correlation does not mean causation. Although an unexpected correlation may lead to a serendipious discovering (source: xkcd)...