What is epidemiology

DEAR DR. BLONZ: You often mention epidemiology when describing research, but I am not sure what that is. Could you give me a brief explanation?

S.F., Seattle

DEAR S.F.: Epidemiology is the science that investigates connections between specific events, such as the occurrence of a disease, and a particular behaviour pattern. In matters of nutrition, this could be an association between diet, exercise and a pattern of health or disease. Epidemiological research can help suggest what’s going on, but it cannot tell you what’s causing what with any precision. Some findings can be informative and on target, while others may only be coincidental.

For example, one study had found that inner-city children suffering from iron-deficiency anaemia were more likely to have lead poisoning. The study showed that these items were connected, but it couldn’t say what was causing what. Innercity residents often have a greater exposure to lead, which could be present in peeling leadbased paints. So, did the lead causing the anaemia, or was it the other way around?

Additional studies filled in the blanks by providing a plausible mechanism behind the relationship. In this case, it was discovered that that low blood iron (anaemia) facilitates lead absorption. This is an example of epidemiology at work, but studies can also uncover strange relationships. One of my favourites, uncovered while in graduate school, came from a list of statistically “connected” phenomena. There was a finding that physicians who eat more meat and consume more alcohol have one-third the risk of dying in a plane crash. So, does that indicate that it’s legitimate science to encourage doctors to grab a burger and a beer before they board their flight? Hardly.

In that case, as in all others, we need to understand a plausible mechanism before giving full credence to results from epidemiology.