The fact that lead is poisonous is definitely taken by the government seriously, and for quite some time. The hypothesis that crime is caused by lead is not, and it is not proven by correlation. I bet if you scan through millions of data series available on everything from wool production in New Zealand to average thickness of hairs of dogs in the USA, you could find a series that correlates very well with the crime data over the last century. Did you know, for example, that US stock market is driven by butter production in Bangladesh? Here it goes: http://money.cnn.com/magazines/moneymag/moneymag_archive/199... http://business.time.com/2009/04/16/the-bangladeshi-butter-p...

Scientific proof of the cause IMHO needs much more than even very nice correlation.