Generally, people are not very good at evaluating evidence from everyday observations. We often see patterns that aren't there and jump to conclusions. Apparently, this now passes as investigative journalism for TV3, whose 3D program gave the very delicate issue of vaccine safety a disastrous treatment on Monday night.

Let me illustrate my point about conclusion jumping with a toy example. Say, you get a new cat. Shortly thereafter, you develop a rare disease named Possibly Cat Disease (PCD). Because the PCD happened after you got a cat, it might occur to you that the cat caused your disease, because that was a recent, noticeable change in your life. This conclusion might be true, but it might not be.

To find out, you might seek scientific studies that have looked into this alleged link between cats and PCD. Scientists carefully collected data from lots of people with and without cats, and compared the rate of PCD between the two groups. If PCD occurred significantly more often among the cat owners, you have evidence for a link between cat ownership and PCD. (Note, this is still not evidence that cats cause PCD per se - just that they are associated. The association could be caused by something else, like having catfood in your house. Establishing cause requires further science).

On the other hand, you might instead ask around your community and discover that a few people with cats have PCD. You might then do some 'research' online and find anti-cat websites and videos showing hundreds of people that contracting PCD after getting a cat. You may talk to grieving mothers who resolutely blame their cat for their child's tragically fatal case of PCD.

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However, this does not constitute evidence. What if, for all the hundreds of cat owners with PCD, there were thousands of non-cat owners with PCD? Real evidence comes from comparing rates of the disease among cat owners and non-cat owners. For the comparison to be valid, the data need to be collected using a scientifically robust method. Looking only at anecdotes of cat-then-PCD can tell us very little.

3D's 22-minute piece, entitled Cause or Coincidence, focused on four unfortunate young women with crippling diseases, and two who had died. They, like thousands of other girls in NZ, have had the human papillomavirus (HPV) vaccine, which reduces the risk of cervical cancer.

The majority of the piece is taken up with Paula Penfold interviewing the girls and their families.

It was shocking and sad, in more ways than one. When asked, some of the girls and parents were convinced that the vaccine was the cause, though some, to their credit, were not. Either way, as much as we feel for them, they are not in a good position to make that judgement. Regardless, Paula Penfold seemed very intent on obtaining these emotive sound bites.

The science, on the other hand, barely got a mention.

There is no credible scientific evidence for the HPV vaccine increasing the risk of these, or any other, serious diseases or sudden deaths. And there has been plenty of science. For example, in 2013, this BMJ study looked at nearly one million girls in Denmark and Sweden. If an association exists, this study, or one of the many others from around the world, would almost certainly have found it. And no, the study was not funded by drug companies (see footnotes to the BMJ article).

Even if TV3 were intent on ignoring the science, why not provide some balance by interviewing families grieving for those lost to cervical cancer? How about mentioning the non-vaccinated girls with the same diseases as those in the story?

The anti-vaccine movement are lapping up TV3's story and posting it all over social media. People will be drawn to their fanatical websites, which present thousands of sad and scary anecdotes. Sometimes they dress these anecdotes as science by quoting big numbers and making graphs.

This is called pseudoscience, because it has no scientific credibility. Unfortunately, the Information Age also provides platforms for misinformation. Their claims imply that the global medical profession is trying to kill you for a profit. This is simply preposterous.

Vaccines are an obvious target for the blame of frustrated and grieving families. But that doesn't mean that a one-sided selection of even thousands of anecdotes constitutes reliable evidence. Such evidence can only be provided by well-designed scientific study.

I urge the New Zealand public, when deciding on what to believe and whether to vaccinate your children, to place greater weight on the real science and try to ignore the pseudoscience. The scientific evidence here is quite clear, and it comes from literally over a million cases. In the face of it, a few emotive, cherry-picked anecdotes should not persuade you.

Cause or coincidence? TV3's story barely establishes coincidence. It certainly doesn't show correlation. The idea of cause is laughable.

If this is the quality of so-called investigative journalism on TV3, we're better off without it and we should let it die. The sad reality is that this shoddy journalism will likely result in some avoidable cases of cervical cancer, which may lead to the same fate.

Adam Smith is a lecturer in statistics at the Institute for Natural and Mathematical Sciences, Massey University