a "scientific" way lol novody has ever done thie not even studies that are fundamentally about penile health. you sound like sone mad man on crackYou have no idea what you are talking about. The finasteride trials and not designed to actually find occurrence of sexual sides. If they were you'd see them measure how quickly it takes to achieve maximal erection with normal stimuli and how long the male is able to maintain erection without any stimulus. THAT would be scientific. Not asking the participants of the study if they experienced any sexual sides in a self report questionnaire.
The fact that most men don't notice they are losing hair until they've lost 40% density just shows that the majority of men are terrible at spotting subtle changes in their body.
If they actually measured sexual performance in a scientific manner then the occurrence of sexual side effects would be almost 100%