OK so the answer is I don&#x27;t understand drug testing :)<p>My understanding was: you need the placebo to compare to to counter out the placebo effect (i.e. if you only test &quot;real drug vs. nothing&quot;, the real drug might show an improvement purely due to placebo and have no actual effect itself). But introducing more variables... surely there are lots of other variables there regardless? If you ran a test of &quot;placebo vs. nothing&quot; what variables come in that wouldn&#x27;t be there for &quot;placebo vs. drug&quot;?