Recently, Reuters released an article with the headline, "Cannabis Bigger Cancer Risk Than Tobacco."

The article was based on a study, to be published three days later, that would prove that statement correct. But as Paul Armentato of AlterNet points out, the Reuters report was based on just the press release on the study, and not the study itself.

Upon investigation, Armentato found that the study's control group consisted mainly of cigarette smokers, undermining any hard claims against marijuana itself causing cancer.

But the real meat of Armentato's critique is his indictment of how the mainstream media fail to review their own previous reports. Just 18 months ago, the same outlets that reported on this study reported the direct opposite. For example, this from the Washington Post: "The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer."

I'm not here to make a case for or against marijuana, which has plenty of advocates and detractors on both sides of the health debate. But if we expect the mainstream media to report accurate, well-researched material with acute analyses, a radical contrast like this is a real wake-up call.

Naturally, changing one's position once new information is uncovered should be allowed. Just think of the attacks John Kerry suffered for changing his mind about the Iraq war. Had the mainstream media treated that story more favorably, the past four years might have been very different.

But shouldn't they at least acknowledge the past reports, instead of merely reporting on the latest findings as if the daily news exists in a vacuum?

Naturally, the marijuana/cancer story may not carry the weight of a presidential election, but it isn't of any small consequence either. Not only do plenty of people smoke pot, but this should sound an alarm about how truth gets determined by our media.

As Charlie (Citizen) Kane, in Orson Welles' great film about a newspaper tycoon, barks to his wife about his influence over the public: "They'll think what I tell them to think."

Let's not let Kane's fascist remark describe those who deliver us the news.