Is there proof that parachutes actually work?
Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials
There are no randomised trials proving parachutes work, so technically the evidence is “weak”.
The authors searched the medical literature for randomised controlled trials comparing jumping out of planes with and without parachutes. They found none.
The joke has a point: some things are obviously effective and don’t need a trial. They cheekily suggest that the most hardcore evidence purists volunteer for the first one.
Sometimes common sense is a valid study design.