Monday, February 26, 2007

Reasoning from personal experience: how lack of experience leads homebirth advocates astray

Reasoning from personal experience is a vitally important skill. For hundreds of thousands of years of human history, it was essentially the only way to reason since there was no written documentation of anything and no scientific study. Reasoning from personal experience can lead us astray, and that is especially obvious in today's world where assertions about past events can be checked against documented historical data, and where massive numbers of events can be aggregated by statistical methods to produce far more accurate assessments.

Erroneous reasoning from personal experiece can be something as trivial as having a pair of "lucky" socks. Something special happened once when you wore the socks and now you deliberately wear them when you are in need of good luck. Rationally, you know that wearing the socks cannot make things happen, but the mental connections created by personal experience are difficult to shake.

Reasoning from personal experience is biased by things that people never think about. For example, it is common for homebirth advocates to say that "if birth weren't safe we wouldn't be here". Not only is that statement wrong from a statistical point of view (since many women and children can die in childbirth and the human species can still survive), but it also suffers from a serious flaw in logic. Yes, "we" are still here. However there are untold millions, perhaps billions of people that would be here if an ancestor had not died in childbirth. Every time a woman or baby dies in childbirth, their putative descendants --- children, grandchildren, and all other future generations --- are obliterated along with them. So the fact that "we" are here tells us nothing about death in childbirth since anyone who died has no descendants to report personal experience of death in childbirth.

Reasoning from personal experience is a particular problem in the homebirth movement. The inherent problems from reasoning from personal experience are magnified by the fact that homebirth advocates, and even homebirth practitioners have very limited experience of birth. Fortunately, modern obstetrics has succeeded in lowering maternal and neonatal mortality rates to very low levels. Therefore, in order to have personal experience of a maternal or neonatal death (as participant or practitioner), you'd need to seem hundreds, perhaps thousands of births. In this country today, most women have 2-3 children. It is unlikely that either they or their children will die. They have the personal experience of safe homebirth, but that actually tells us nothing about the safety of homebirth. Similarly, homebirth midwives rarely deliver more than a few patients a month. At that rate, it could take decades to be confronted with a poor outcome. A midwife may pride herself the healthy outcomes of the homebirths that she attended; but in reality, the fact that all of the outcomes were good is just because she hasn't attended many deliveries.

That's why the perceptions of obstetricians about the risks of childbirth are likely to be much more accurate than those of lay people or homebirth midwives. After you've seen a thousand deliveries, you have a much more accurate idea of what can happen in childbirth.

So when it comes to homebirth, reasoning from personal experience on the part of lay people or homebirth midwives is more likely to lead to faulty conclusions than not. For this reason (and others) statistics are the only reliable method for accurately assessing risk.

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