As someone who is fascinated by the systematic analysis of health risk data I sometimes look at the health pages and try to work out what they're supposed to do.

This week, for example, you'll have found: "Teenager helps his twin brother by donating a piece of his back"; "Taking antibiotics to prevent premature birth can 'increase risk' of cerebral palsy"; "Why drinking water to shed weight is a waste of time"; and "More men suffering from 'Manorexia', health experts warn".

Are people clipping these stories out, and pasting them in indexed files, ready for the day when they develop the condition in question? And how will they know if the data is complete, or just an arbitrary patchwork of newsworthy and self-serving information, multiply filtered through a range of imperfect agents with diverse interests and allegiances? In fact, how does anybody know that?

This week the media ignored a study looking at that exact question. It was also one of the most important papers to be published this year: only one in five trials on cancer treatment actually gets published; the rest are missing in action. And it gets worse: only 5.9% of industry-sponsored trials on cancer treatment get published. Later, it will get worse again.

For decades people have known that negative results tend not to get printed in academic journals, and it can happen for all kinds of reasons: they're not newsworthy, they're not much fun to write up, they don't look good on your CV, and they might not flatter your idea or product.

One suggestion which I bang on about incessantly is that all clinical trials should be registered before they begin: then people stand a chance of noticing if and when a trial goes missing in action. This took about 20 years to be put into practice. But there is a problem: who will chase up the missing studies?

Scott Ramsey, from the Fred Hutchinson Cancer Research Centre in Seattle, and John Scoggins, of the University of Washington, Seattle, took on the role of investigative journalists. In a world where not one person from the world of alternative therapies can bring themselves to criticise even vitamin pill entrepreneur Matthias Rath for his dangerous practices in South Africa - indeed some still support him, as we may soon see - critical self-appraisal is simply business as usual in academia. They went to clinicaltrials.gov, the register run by the US National Institute for Health, and found all the trials on cancer: 2,028 in total. Then they went to Pubmed.gov, the searchable database containing almost all the medical journals. The majority were missing. Only 17.6% were published, but 64.5% of those reported positive results. How impressive. Meanwhile, only 5.9% of industry-sponsored trials were published, but in those 5.9%, golly did they do well: 75% gave positive results.

We may never know what was in that unpublished data, but those missing numbers will cost lives in quantities larger than any emotive health story covered in any newspaper. Doctors need negative data to make prescribing decisions. Academics need to know which ideas have failed, so they can work out what to study next, and which to abandon. In their own way, academic journals are exactly as selective as the tabloid health pages. God help us all.