Smoker's Risk by DNA

The NYT has a smaller article in today's Saturday edition that has a great example of the problems with the basics of correlation versus causation. The Synergenz study discussed in the article state that the scientists took a sample of 239 smokers with lung cancer and 200 without, and used that sample set to find the 20 genetic variations most correlated with the presence of the disease.

To 'validate' these results, the team then followed individuals with chronic obstructive pulmonary disease around for 4 years, finding that those who developed lung cancer were more likely to have been given high risk scores by the test. COPD's leading cause is smoking, but my problem is nowhere in this article does it say that the individuals followed with COPD were also smokers.

While it makes a very nice argument for likely factors indicating higher risk of lung cancer for smokers, the article does not make a very clear distinction between correlation and causation. Further, 4 years is a short time frame, relative to the average age of humans, to draw accurate conclusions. It would be interesting to see, over the span of 10 or 15 years, how the results of the study held up.