Wednesday, April 1, 2009

When epidemiology works

Sometimes epidemiology produces a reasonable result. Take this recent story.

Researchers note that somewhere has a very high rate of a relatively rare condition. In this case a province of Iran with a high rate of oesophageal cancer. The first step in such a situation is often the case control study. This is a study done on the basis of matching people already diagnosed with the condition as closely as possible with controls who do not have the condition and then attempting to find significant ways in which the cases and the controls differ. Case control studies can be problematic because the results can be manipulated by choice of the controls. Also this type of study is purely observational and it is after the fact observation. You are relying on people's recall and what they recall may be influenced by their present condition - particularly when they have a serious disease. However in this study the results were quite striking:

Compared with drinking warm or lukewarm tea (65C or less), drinking hot tea (65-69C) was associated with twice the risk of oesophageal cancer, and drinking very hot tea (70C or more) was associated with an eight-fold increased risk.

The speed with which people drank their tea was also important.

Drinking a cup of tea in under two minutes straight after it was poured was associated with a five-fold higher risk of cancer compared with drinking tea four or more minutes after being poured.

There was no association between the amount of tea consumed and risk of cancer.

Compare this with the purported increase in risk of death from eating red meat (based on the responses to one labyrinthine food frequency questionnaire ten years earlier) of about 0.31 times (men) to 0.36 times (women).

And what was also nice was that having asked people to estimate how hot they drank their tea, they then went and measured the actual temperature.

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