Above all, [smoke-free] policies contribute decisively to denormalise smoking, and help with the approval and implementation of other policies that reduce tobacco demand, such as increased tobacco taxes and a comprehensive ban of tobacco advertising, promotion, and sponsorship.
Still, you can't fault their impeccable methodology:
To identify national data for second-hand smoke, the keywords “second hand smoke”, “environmental tobacco smoke”, and “passive smoking” were combined with names of countries or regions, by searching Google and the PubMed database
The spirit of Newton and Darwin lives on, does it not?
What can be said of the 600,000 estimate? Obviously if you extrapolate a relative risk over a larger population, you will get a larger number. That doesn't make the study or studies you are extrapolating from any better, but I won't risk waking this blog's resident troll by going into all that again.
It's interesting that this study appeared in the Lancet because back in the 1990s, Lancet columnist Petr Skrabanek* remarked on the tendency of public health campaigners to use larger and larger populations to get scarier and scarier death counts. He called them "jumbo-jet numbers" because talking about the equivalent number of jumbo-jets that would have to crash for the same death toll sounds more dramatic than explaining that you have to die of something and that most of the people being "killed" were very old. This, from a collection his articles [PDF]:
The intoxication with numbers is another characteristic of the modern crusaders against smoking. They typically use big population blocks as denominators to obtain bigger and bigger numbers. Richard Peto, a leading anti-smoking exponent and a statistician, announced that 'of all children alive today in China under the age of 20 years, 50 million will eventually be killed by tobacco.' This would put the hecatombs of the Second World War in the shade. The British Medical Journal referring to another such statistic, 'typical of the Oxford epidemiologist Richard Peto', quoted that 'about 20 million children now living in Europe will be killed by tobacco in their middle age.' And The Times reported on January 1, 1988, that according to Mrs Risk-factor Epidemiology: Science or Non-science?
Edwina Currie, 'more than a million schoolchildren and 60,000 babies born this year will die of smoking-related diseases such as lung cancer.' Surprisingly, no-one has yet used the population of the whole world as a denominator: this would produce numbers of babies, toddlers, schoolchildren, and other children, killed by tobacco in truly phenomenal ranges. Perhaps the reason for this reticence is the fear of overkill.
Well, now they have. In fact, they've missed a trick by not using the other PR tool of multiplying by years (eg. here). So, to save someone the trouble, here's my study:
'A quantitative, longitudinal assessment of worldwide mortality from environmental tobacco smoke'
Christopher J. Snowdon
Methodology: Google and PubMed of course. I'm a professional.
Results: 600,000 x 10 = 6,000,000
Conclusion: Secondhand smoke will kill 6 million people over the next ten years. Where's my cheque?
[*nb. Petr Skrabanek was a skeptic about—amongst many other things—secondhand smoke. You can probably guess what the anti-smokers' response was. That's right, they accused him of working for the tobacco industry. Which was a lie. He died of a non-smoking related disease in 1994.]