In May 2003, the British Medical Journal published a study by James Enstrom and Geoffrey Kabat that claims to find only a weak association between secondhand smoke exposure and heart disease and lung cancer.
The study was funded by the now-defunct Center for Indoor Air Research, which was created by several tobacco companies for the stated purpose of perpetuating the idea that there is a controversy about the dangers of secondhand smoke.
The cohort study looked at mortality from heart disease or lung cancer in non-smokers who were married to smokers, which covered a time period from 1959 to 1998. Some of the critical flaws include not measuring for secondhand smoke exposure from any source other than the spouse, not even the workplace, where smoking was extremely prevalent at the time; not taking into account either spouse's smoking status after 1972, though the study continued for 26 more years; and classifying the non-smoking spouse as still exposed to secondhand smoke throughout the 26 year period, even though the "smoking spouse" could have quit smoking, died, or moved out.
Click here to read more about Enstrom and Kabats' relationships with the tobacco industry.