In Non-smoking wives of heavy smokers have a higher risk of lung cancer: a study from Japan, a paper published in the British Medical Journal in 1981, Dr. Hirayama set up an observational study to see if second hand smoking is related to lung cancer. From 1966 to 1979 (14 years), Dr. Hirayama tracked the prevalence of lung cancer in 91,540 non smoking wives aged 40 and above. He categories the smokers (and non smokers) into groups of different amounts of cigarettes and compares the prevalence of lung cancer in the wives of these smokers between these different categories of cigarette usage. With a p value of 0.00097, Dr. Hirayama concludes that the wives of smokers have a statistically significant higher risk of lung cancer than the wives of non-smokers do; sequentially, he reports that, although not as much as first hand smoking, second hand smoking causes lung cancer.
In the way and manner this paper is written, finding out that second hand smoking can cause harm seems to be shocking and somewhat cutting edge. This study probably reached headlines and causes many a smoker to quit on behalf of the health of their loved ones; this, of course, is a good thing because it most likely reduced the number of smokers in the world, decreasing the potential years of life lost globally. On top of that, companies can produce and develop alternative methods for nicotine addict to get their fill of nicotine without lighting up and causing second hand smoke (which I think could have stimulated the economy).
Of course in order to include so many subjects in the study, Dr. Hirayama had to do an observational study. He couldn't, with relative ease, create a true experimental study. Doing an observational study would have been the best choice economically and logistically.
But the main problem of doing an observational study is that there are many more variable which are not controlled which causes the association to not immediately mean causation.If we look at Hill Criteria for causation, all the criteria checks out (strength of association, consistency of association, high number of subjects). Just like the study that concluded that coffee caused pancreatic cancer with a significantly low p value (when it was really caused by tobacco), the association found in this study may be cause by a confounding factor(s). For example, husbands who smoke may be more depressed, and this depression is shared with the wives, which in turn causes a pathway that leads to lung cancer; or perhaps, smoking husbands have less disposable income, so the wives are more stress in the accounting department, which causes lung cancer. I do believe that that second hand smoke causing lung cancer seems to have a logical biological pathway, but there could still be a middle man factor that is the actually cause of lung cancer.
In any case, it may be better for wives, kids, husbands to reduce cigarette consumption for their own and the health of other. If needed be, those who really needs the buzz or effects from nicotine have many alternatives to cigarette to chose from nowadays; There are electronic cigarettes, nicotine patches, and gums. Of course they are relatively new and the long term effects of using them are not known yet, but, without a doubt, they don't produce second hand smoke that causes harm to people other than the user.