Some people are invisible. Not really to eyes and such, but invisible in studies and statistics, we know nothing about them. They’re the dark matter of humans, but please don’t call them dark humans.
Suppose there was a gene, let’s call it gene X, that predisposes you never to participate in any study as a subject. It makes you decline all requests to record your data for research purposes and refuse to ever vote for anything.
Carriers of gene X might be at increased risk for cancer. They might be invulnerable to hemlock. They might all individually have an IQ of exactly 120.2. Maybe they never forget where they left their keys, or grow an extra belly button during their third puberty. Possibly they’re all called Alex and stop aging when 50 years old, only to suddenly die on the day they turn 90 years old. Hell, they might be 20% of the world population, favour the Libertarian Party and think Estonia should have won the last Eurovision song contest. We’d never know because nobody can study them.
On the other hand: suppose there is some subpopulation that always participates in studies, and forms a big fraction of participants in nearly any study. It makes sense to want to be a part of this subpopulation, because that way every study ever will be more descriptive of you. Luckily, you can become part of this group simply by committing to participate in every study you are asked for from now on. Except that reading this post might have caused you to make that commitment while you would never have done so yourself. You can now only become part of a new subpopulation, the one that commits to being studied after reading a participation bias-based suggestion to do so.