A quick trip on Google scholar turns up a lot of studies on the size of male erections.

https://static1.squarespace.com/static/553598c1e4b0a7f854584291/t/55ee4a5ee4b025d99f73150e/1441679966732/Penis+Size+Study+-+Veale+et+al+2015+BJUI.pdf

It is acknowledged that some of the volunteers across different studies may have taken part in a study because they were more confident with their penis size than the general male population.

Ha, poisoned data tho

a researcher can’t be in the presence of a sexually aroused erect penis

Is this some puritan rule? Plenty don't care to flap their erect penis in the faces of some researchers if they asked nicely. What got ethics to do with it when there is consent?

It depends on the specifics of the experiment. Throughout the 20th century, the people most keen on unethical medical experiments seemed the least able to design useful experiments. Sometimes people claim that we learned lots from the horrific medical experiments taking place at Nazi concentration camps or Japanese facilities under Unit 731, but at best, it's stuff like how long does it take a horribly malnourished person to die if their organs are removed without anaesthesia or how long does it take a horribly malnourished person who's been beaten for weeks to freeze to death, which aren't much use.

Eh, usually less than you would expect. We're really good at math and are quite capable of making synthetic experiments where we find people who either require the procedure, or where it's been done incidentally and then inferring the results as though deliberate.

We can also develop a framework for showing benefit from the intervention, perform the intervention ethically, and then compare that to people who didn't get the intervention after the fact. With proper math you can construct the same confidence as a proper study without denying treatment or intentionally inflicting harm.

It's how we have evidence that tooth brushing is good for you. It would be unethical to do a study where we believe we're intentionally inflicting permeant dental damage to people by telling them not to brush for an extended period, but we can find people who don't and look at them.

That's actually pretty the whole premise of The Vital Abyss short story. Cortazar explains how he signed up with Protogen and how glad he was to get the nerve staple that removed all empathy from him. Ot, and all the other short stories are worth reading if you liked The Expanse

"You're not that guy"

...

"I am that guy 💥"