Monday, March 05, 2007

Lay epidemiology and risk assessment

I have often noted that homebirth advocates and DEMs lack background in and understanding of the scientific method and statistics. That does not mean that lay people do not try to make sense of medical events that occur to them. These attempts to understand why diseases or medical complications happen to specific people in specific instances has been termed "lay epidemiology". This is to distinguish it from the discipline of epidemiology that looks at the occurence of health and illness in large populations.

In Thinking about risk. Can doctors and patients talk the same language? Misselbrook and Armstrong note that doctors and patients have very different ways of thinking about risk:
First we must recognize that patients have their own risk models. These bear little relation to the mathematical risk models used by doctors. Davison and his colleagues found that the lay classification of risk was based on a polarity model rather than the gradation of a continuing spectrum. People saw themselves as either high risk or low risk. This model identified ‘likely candidates’ for illness. Thus a beer-swilling heavy smoking overweight man would (rightly) be seen as at high risk of a heart attack. However, if he did not have a heart attack and his healthy living neighbour did, Davison found that a second element in the lay risk model came into play. Luck, fate and destiny were also perceived to determine health outcomes.

Remember, John Everyman wants to know whether he himself is going to have a heart attack, and my mathematical model will not tell him. If we are not talking about populations but about individuals, then a high risk/low risk model feels like a better fit. It provides the patient with a map to enable them to function and to cope in an uncertain and threatening world.
In other words, doctors think about risks in term of numbers. An excess risk of neonatal mortality at homebirth of 1-2/1000 means that 1-2 babies will die unnecessarily at homebirth and that the tragedy of neonatal death could befall any patient. Patients, on the other hand, have a very different understand of what this means. They do not realize that the risk is spread throughout the population and tend to think that bad outcomes happen only to high risk people. Judging themselves to be low risk, they think that it is exceedingly unlikely that a bad outcome can happen to them, and that if it does happen, it is because of fate ("some babies are meant to die").

Simply put, doctors know that the risk of excess neonatal death means that anyone can lose a baby at a homebirth. Patients on the other hand, while aware of the risk, think that it doesn't really apply to them. Couple that with the fact that doctors have seen so many patients that they have direct personal experience with neonatal death, while most patients don't know anyone who lost an otherwise healthy baby, and you can begin to see how doctors and patients talk right past each other when discussing the risk of homebirth.

Doctors see the risk of homebirth as small, but real. Patients, on the other hand (particularly homebirth advocates), tend to believe that they are not at risk for the bad outcomes, so in their minds, the small risk is essentially no risk.


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