No significant difference...may...might...possibly....

The World Health Organization is fervently anti-smoking; their goal is its complete elimination. In 1975, before any major studies had been conducted on SHS, the WHO recommended that the goal of anti-smoking activists and health organizations should be to lead the public to believe that secondhand smoke is harmful to nonsmokers. The WHO finally conducted a study on the matter in 1998.

No doubt confident they could "prove it," the study was actually a textbook example of the right way to conduct an epidemiologic study. It was a case control study using a large sample size and was conducted from twelve centers in seven European countries over a period of seven years.

We can only speculate that the WHO was horrified by their results: that no statistically significant risks exist for nonsmokers who live or work with smokers. In fact, the study's only statistically significant result was that secondhand smoke has a protective effect on children!

To reiterate, the study was large, its methodology was sound, and it was conducted by an organization full of anti-smokers who had every motivation to "prove" that secondhand smoke was dangerous.

The results were the opposite of what they must have been hoping for, and they certainly wouldn't help them "to foster an atmosphere where it was perceived that active smokers would injure those around them."

The WHO tried to bury the study, but it was eventually discovered by the press:

"...the science fell off the campaign wagon two weeks ago when the definitive study on passive smoking...reported no cancer risk at all. Don't bet that will change the crusaders' mind. The anti-smoking movement, after all, has slipped from a health crusade to a moral one. It is now obvious that antismoking activists have knowingly overstated the risks of secondhand smoke."--the Wall Street Journal

In response to revelations about their study, the WHO issued a press release titled "Passive Smoking Does Cause Lung Cancer - Do Not Let Them Fool You." Yet, the release had no science to back up its title (which in effect was the exact opposite of what their study showed). The WHO also neglected to mention the study's one statistically significant result--that SHS has a protective effect on children--which you'd think an organization whose goal was to protect health would want everyone to know.

Tellingly, this WHO study is often offered to legislators as "proof" by anti-smokers, who know that most politicians are unfamiliar with the true meaning of its results!

The "problem" of being unable to link SHS to lung cancer had to be corrected, however, so the WHO conducted another study. But it was different from the first one: it was a meta-analysis, which are generally considered to be dubious because they allow those performing the study to cherry-pick data to achieve whatever results are desired.

Such practices are now standard procedure when it comes to secondhand smoke studies. The only way anti-smokers can achieve their stated goal of making smokers seem dangerous to others is by ignoring all overwhelming indications to the contrary.