In medicine, level of proof is a sliding scale which you can arbitrarily choose depending on what you wish disproven

In medicine, level of proof is a sliding scale which you can arbitrarily choose, depending on what you wish disprove
Observational studies are no proof unless they prove what you want proven. RCTs are proof unless they disprove what you don’t want disproven.n

The PLCO trial compared PSA testing with PSA testing and found, unsurprisingly, that the group which received PSA testing didn’t live longer than the group which received PSA testing.