Global temperatures have steadily risen over the past 150 years and the number of pirates has declined at a comparable rate. No one would reasonably claim that the reduction in pirates caused global warming or that more pirates would reverse it. But it’s not usually this clear-cut. Often correlations between two things tempt us to believe that one caused the other. However, it’s often a coincidence or there’s a third factor causing both effects that you’re seeing. In our pirates and global warming example, the cause of both is industrialization. Never assume causation because of correlation alone – always gather more evidence.