For example, there is overwhelming evidence that smoking cigarettes causes lung cancer, yet many smokers never get lung cancer, and many non-smokers die from the disease. Even with decades of research, the causes of many diseases are not absolutely certain, and any given individual's chance of getting a disease is influenced by dozens, or even hundreds, of different factors ranging from genetics to diet to lifestyle - and a lot of random-chance, good, old-fashioned luck.
It is true, as Chavez noted, that leaders of several South American countries have battled cancer in recent years, including Argentina, Paraguay and Brazil. The fact that several of these presidents, unlike Chavez, are friendly to the United States - and that leaders of 10 other countries on the continent are cancer-free - suggests that the accusation is more informed by paranoia than reason. Given how pervasive cancer is, a cluster among this group would not be extraordinary.
Still, we are talking about a fiery, demagogic leader who once claimed during a 2006 speech at the United Nations that he could still smell the stench of Satanic sulfur left over from when George W. Bush had been in the room a day earlier. Whether or not Chavez truly believed that his cancer had been caused by the United States, he knew it made good rhetoric.