This post might be more for the casual reader than skeptics and Bad Science bloggers. I’m sure they will already know far more about epidemiology than I do. Here we go anyway:
From time to time, I see criticism of epidemiology and the use of statistics. Usually on the basis that epidemiology “can’t prove anything” or is “not real evidence”. Sometimes a seemingly opposite tack is used: “oh, but you can use statistics to prove anything”. The criticism usually comes from someone whose own particular worldview is being challenged. Like, for instance, Dave Hitt. Dave Hitt features in this post on the Apathy Sketchpad blog. Or for another example of the statistically-challenged, there’s Gus from the JABS forum. [“Why is it you never listen to the evidence (the autistic children) and are only interested in the science and epidemiology provided by tabloid gutter press as it was hardly hard to see where the research had come from?”]
So what’s epidemiology ever done for us? There’s a couple of chaps I’d like you to meet first: Richard Doll and Austin Bradford Hill. Now quite apart from anything else Bradford-Hill did, he encouraged use of controlled trials (PDF) – something important in its own right. Bradford-Hill also helped to show, along with Doll, the part that tobacco smoking played in lung cancer. The original Doll/Bradford-Hill paper is available via Pubmed here and here as a PDF [which might take a while to download]. The authors concluded that “smoking is an important factor in the cause of carcinoma of the lung.” It’s now accepted (almost universally) that smoking is harmful – but how long might it have taken without the work of Doll and Bradford-Hill? Can you imagine what might have been if Doll and Bradford-Hill’s work had been ignored by a nation of Dave Hitts?
Another example of the usefulness of epidemiology and statistics is in the epidemiological approach to another notable condition. In Lange’s Medical Epidemiology (Third Edition – the Fourth Edition is available*), there is a description of a young man with no obvious underlying causes of immune dysfunction who is suffering from three concurrent infections. Within the preceding six months, three other patients with similar symptoms had been referred to the UCLA Medical Center. Other, similar reports were received by public health authorities and the CDC set up a task force to collect detailed information on those affected. Within months, the disease was named the acquired immune deficiency syndrome (AIDS).
Epidemiological methods were used: to monitor the patterns of the occurrence of AIDS; to measure the rapidity of occurrence; and to search for causes by identifying risk factors. They were also used in determining case fatality, survival time and prognostic factors. Which I would have thought were all important things to know. Lange’s Medical Epidemiology tells us that “medical progress often is best advanced when the sciences that focus on subcellular and molecular basic research work in tandem with the population-oriented science of epidemiology. For example, as bench scientists were struggling to characterize the molecular properties of HIV, epidemiologists already determined that AIDS is a contagious disease that is spread through certain interpersonal behaviours. As the painstaking search continues for improved treatment, or even a cure or vaccine, public health professionals have recommended measures to prevent the spread of HIV by reducing the frequency of the fololwing high-risk practices: (1) casual, unprotected sex and (2) sharing needles among drug users.”
Cardiff University has a page with links to lists of Bradford-Hill’s principal publications and literature related to Bradford-Hill.
*McGraw-Hill Medical Publishing Division seems to be here, and the Fourth Edition of Medical Epidemiology is available here.