Smokin' ...?

I'm not encouraging you to smoke, but scary headlines like “Smokers seven times more likely to get lung cancer” on a report by Salma Khalik of the Straits Times needs to be decoded:

Extracting the data:
population was ethnic Chinese
studt lasted 25 years from 1993 to 2007
45900 were tracked over this period
33292 did not smoke
over 25 years, 463 people were diagnosed with lung cancer
25.5% of these were non-smokers, or 116 by my calculation

Let's do some primary school arithmetic, shall we?
smoker population was 12698 (45900 – 33292 = 12698)
smokers getting lung cancer – 347 (463 -116 = 347)

Now we can decode the scary headline: Over 25 years, and not for one year:
1.12352 of the 12698 smokers did NOT get lung caneer, or 97.3%
2.33176 of the 33292 smokers also didn't get cancer, or 99.4%

Just to be clear about these numbers, smoking for 25 years increases your risk of geting lung cancer by 2.1% (99.4% - 97.3% = 2.1%). If you are a smoker, and I'm not, you figure if this is an acceptable risk. Just don't let relative “prevalence rates” scare you. You are not “seven times more likely to get lung cancer”.

If smokers are thinking about quitting, they should, of course, consider the effects of smoking on blood pressure, general fitness ... I'm not a registered medical practitioner and cannot give medical advice, just someone, moderately numerate, with a sensitive B.S. Meter.