Monday, April 21, 2008

What does it mean to understand a risk?

Much of the disconnect between homebirth advocacy and obstetrics hinges on the fact that homebirth advocates do not understand the risks involved. Since a woman can only make an informed decision if she understands the risks, it is important to assess understanding. On the face of it, this may seem to be a simple task; either she understands or she doesn't. In reality, the assessment of the understanding of risk is more complex.

Before we discuss the criteria for determining whether a woman understands a particular risk, let us look at the way knowledge of risks is handled in the homebirth advocacy community. The fundamental method for dealing with risk among homebirth advocates is to simply pretend that it doesn't exist. So, for example, the entire homebirth advocacy community engages in a community wide fantasy that homebirth is as safe as hospital birth.

The pretending extends to the realm of specific complications. Homebirth advocates understand that complications can occur, but they like to pretend that risk is an all or nothing phenomenon. In other words, according to the "reasoning" of homebirth advocates, if breech birth were risky, all breech babies would die. Therefore, by this "reasoning", the fact that most breech babies survive vaginal delivery shows that doctors vastly overstated the risks. Of course, no obstetrician would ever claim that the risk of death at breech vaginal delivery involved any more than a small fraction of babies. By deliberately distorting what obstetricians say, and by insisting that risk means death for 100% or at least some large proportion, homebirth advocates can continue to live the fantasy that birth should be "trusted".

These are merely the errors of reasoning made routinely by homebirth advocates. We have not even addressed the fact that homebirth advocates lack fundamental knowledge about the nature and magnitude of most risks. As a general matter, homebirth advocates "understanding" of risk is based on magical thinking and ignorance. In other words, they don't understand risk at all.

How can we tell when someone does understand a risk, and is therefore capable of making an informed decisions about accepting or refusing treatment? Neil Weinstein discusses the criteria in his paper What Does It Mean to Understand a Risk? Evaluating Risk Comprehension, published in Journal of the National Cancer Institute Monographs No. 25. Weinstein suggests that the knowledge needed for understanding of risk can be group into three categories: "the identity and severity of the potential harm, the likelihood of harm under various circumstances, and the possibility and difficulty of reducing that harm.

As Weinstein states:
Judging the severity of a hazard requires more than a vague understanding that an activity is "bad for you" or that it "causes cancer." Unless a person has a reasonably complete knowledge of the undesirable consequences of that activity — both what outcomes can occur and how serious these outcomes are — he or she is not in a position to decide how negative the consequences might be.
In the case of childbirth risks, homebirth advocates fail to meet this most basic criterion. Indeed, rather than having a reasonably complete knowledge of undesirable consequences of a particular choice (such as breech vaginal delivery), homebirth advocates pretend that there is no increased risk, have literally no idea of the magnitude of the risk (because they are pretending it is zero), don't understand the factors that increase or decrease the risk, and don't understand the negative consequences.

Homebirth advocates are not alone in their failure to acknowledge real risks.
Quite a few studies have asked smokers how their risk of becoming ill from smoking compares with the risk of the average person ... Ayanian and Cleary found that 71% of smokers believed their personal risk of heart attacks to be average or below average when compared with the risk of other people of their age and sex, and 60% believed that their personal risk of cancer was average or below... In no case did smokers acknowledge that their risk of lung cancer, heart disease, or emphysema was "moderately," "substantially," or "much" higher than that of the
average person...
In other words, those at increased risk are the people who are least likely to understand and acknowledge the risk.

... Chapman et al. found that smokers maintain a constellation of comforting, risk-minimizing beliefs. About one third of smokers, for example, agreed that "Many people who smoke all their lives live to a ripe old age, so smoking is not all that bad for you..."
Homebirth advocates practically specialize in "comforting, risk-minimizing beliefs." These range beliefs that nutrition can prevent complications to beliefs that pretending you won't have complications (birth "affirmations") can prevent complications.

Homebirth advocates are very much like smokers when it comes to risk minimizing rationalizations.
Research has shown that risk perception is not an unbiased appraisal of information, but rather an attempt to seek the most comforting view of one’s personal vulnerability that fits within the bounds of the evidence. As a result, whatever people believe about the risks faced by others, they tend to believe that their own personal risks are less...

This optimistic bias appears to be equally descriptive of adults and adolescents. The magnitude of unrealistic optimism (i.e., the difference between risk estimates for oneself and for others) varies from hazard to hazard, but it is particularly large for problems, like lung cancer, that are believed to be preventable by individual action.
It is this point that underlies obstetricians negative reaction to women who claim that they "understand" the risks of refusing interventions. Obstetricians, like all doctors, know from research papers and from vast personal experience that lay people routinely misunderstand risk because they assume that bad things won't happen to them. Obstetricians do not believe women who claim that they understand the risks of VBAC or the risks of vaginal breech, because most lay people do not understand the risks of adverse outcomes, and those at greatest risk of an adverse outcome are least likely to understand it.


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