Paul Wermer, CC BY-NC-SA 4.0<p><span class="h-card" translate="no"><a href="https://masto.ai/@Nonilex" class="u-url mention" rel="nofollow noopener noreferrer" target="_blank">@<span>Nonilex</span></a></span> </p><p>“There are no control groups,” Campen said. “Everyone is exposed.”</p><p>And that's a real problem - I recall the story breaking that second hand smoke was contributing to breast cancer - but it took many years of reduced smoking rates before enough women had NOT been exposed to second hand smoke so that they could compare groups in a meaningful way.</p><p>One of the reasons I am heartbroken that the <a href="https://sfba.social/tags/PrecautionaryPrinciple" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>PrecautionaryPrinciple</span></a> has been rejected by the US. By the time you find the harm, and demonstrate linkages, the damage is done.</p>