Denying to the Grave: Why We Ignore the Facts That Will Save Us by Sara E. Gorman

Author:Sara E. Gorman [Gorman, Sara E.]
Language: eng
Format: epub, mobi
ISBN: 9780199396603
Amazon: 0199396604
Publisher: Oxford University Press
Published: 2016-09-02T04:00:00+00:00

Pies That Don’t Satisfy

This brings us to a concept of causality used commonly in epidemiology that is for some reason very difficult to wrap our minds around: the sufficient-component cause model. Invented by epidemiologist Ken Rothman in 1976, this model is the subject of numerous multiple-choice questions for epidemiologists and public health students across the globe every year. As one of your authors with training in epidemiology knows, these are the questions that many students get wrong on the test. They are notoriously complex and sometimes even counterintuitive. The model imagines the causes of phenomena as a series of “causal pies.” For example, obesity might be composed of several causal pies of different sorts. One pie might detail environmental causes, such as lack of a good walking environment, lack of healthy food options, and community or social norms. Another pie might include behavioral causes, such as a diet high in sugar and calories, lack of exercise, and a sedentary lifestyle. A third pie might include familial causes, such as poor parental modeling of healthy behaviors, a family culture of eating out or ordering takeout, and a lack of healthy food available in the home. A final pie might involve physiological factors like genes for obesity and hormonal abnormalities that cause obesity like Cushing’s disease or hypothyroidism. Taken together, these different “pies” cause obesity in this model. For a cause to be necessary, it must occur in every causal pie. For example, if factor A needs to be present to cause Disease X, but other factors are also needed to cause Disease X, then the different pies will all have factor A in combination with other factors. If a cause is sufficient, it can constitute its own causal pie, even if there are other possible causes. For example, HIV is a sufficient cause of AIDS. HIV alone causes AIDS, regardless of what other factors are present.

In this model, causes can come in four varieties: necessary and sufficient, necessary but not sufficient, sufficient but not necessary, or neither sufficient nor necessary. The presence of a third copy of chromosome 21 is a necessary and sufficient cause of Down syndrome. Alcohol consumption is a necessary but not sufficient cause of alcoholism. In order to be classified as an alcoholic, alcohol consumption is necessary, but the fact of drinking alcohol in and of itself is not enough to cause alcoholism, or else everyone who drank alcohol would automatically be an alcoholic. Exposure to high doses of ionizing radiation is a sufficient but not necessary cause of sterility in men. This factor can cause sterility on its own but it is not the only cause of sterility, and sterility can certainly occur without it. A sedentary lifestyle is neither sufficient nor necessary to cause coronary heart disease. A sedentary lifestyle on its own will not cause heart disease, and heart disease can certainly occur in the absence of a sedentary lifestyle.

Although the model may seem abstract and overly complex, it is actually more relevant to everyday life and everyday health decisions than many people realize.

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