Economist.com | Economics focus: "In medieval Holland, it was noted that there was a correlation between the number of storks living on the roof of a house and the number of children born within it. The relationship was so striking that, according to the rules of maths that govern such things, you could say with great confidence that the results were very unlikely to be merely random. Such a relationship is said to be ?statistically significant?. But the Dutch folklore of the time that storks somehow increased human fertility was clearly wrong."