There are two problems regarding celebrity opinion. One is that the media presents such opinion as newsworthy, inflating its legitimacy and confusing it with something akin to expert testimony. The other is that the American public generally expresses interest in what these celebrities have to say about topics that are often far outside the scope of what they can claim expertise in. And even when we know it's bullshit, we still eat up steaming piles of celebrity blather with gusto on a daily basis. Take, for instance, yesterday's revelation in an Associated Press story that Nicole Kidman believes in the existence of magical Australian waterfalls that promote fertility.
Kidman welcomed her first child with singer Keith Urban into the world on July 7, 2008. Roughly nine months prior to this occasion she was on location in the Australian Outback filming the soon to be released epic movie Australia. Kidman believes that there has to be more to her pregnancy than the obvious fact that it is intimately related to her having had sex with her husband during ovulation. She is 41 and the pregnancy was unexpected, six other women who swam in the magic waterfalls near Kununurra, a small town in northwestern Australia, during production got pregnant, and of the seven babies only one was a boy. According to the lovely and talented, if not skeptically minded Kidman, "There is something up there in the Kununurra water because we all went swimming in the waterfalls, so we can call it the fertility waters now."
I'm just a humble skeptic, with no claims of expertise in the epidemiology of fertility, but I am sure that Kidman is not the first somewhat older woman to unexpectedly become pregnant. A quick online search revealed that women at Kidman's age have a 44% chance of becoming pregnant and going on to celebrate a live birth within one year of trying, and 64% will do so within four years. Those numbers aren't great, especially if you are one of the greater than 50% that may be increasingly frustrated with a lack of success, but they aren't bad. Of course, Kidman isn't an epidemiologist or a fertility specialist either. She is a human. An incredibly sexy human. But her preternatural attractiveness doesn't protect her from committing the same errors in thinking that plague us regular folk.
In this case, Kidman has fallen prey to one of the most common logical fallacies around, and one which lies at the heart of a variety of mistaken beliefs ranging from psychic powers to claims of effectiveness by proponents of unproven medical treatments. Post hoc reasoning, more formally known as the post hoc ergo propter hoc (after this therefore because of this) fallacy, occurs when a temporal relationship is confused for a causal one. Just because B follows A doesn't mean that A caused B. It could only be a coincidence, or there may be many factors at play with A only serving a minor role in causing B.
Typically unique experiences benefit from this logical fallacy the most, such as a novel treatment for an illness or a memorable dream of something bad happening. Many herbal supplements and homeopathic remedies achieve word-of-mouth success because they are advertised with claims of treating self-limited maladies like viral illnesses. As I tell my students, you can take [insert OTC supplement] to cure your cold and feel better in a week, or do nothing and feel better in seven days. What personal claims of effectiveness of a treatment, or of getting pregnant after taking a swim, amount to are uncontrolled anecdotes. We don't know what would have happened had Kidman not gone for a swim. It's very likely she would still be celebrating the birth of her daughter, only instead of the magic Australian water she would be praising something else entirely for its fertility boosting effects. Perhaps a new food she ate or a mud bath.
But as it stands right now, it is only a matter of nanoseconds before someone is selling magical Australian fertility water by the bottle, or arranging for fertility boosting baths under the waterfalls. People with too much money, and not enough critical thinking skills, will fly there at great expense to improve the health of their uterus. Somebody is going to get rich off of this, and a lot of desperate women are going to throw good money down the drain.