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You should look for high-quality sources, like a randomized controlled trial (RCT) or systematic review, to answer your foreground question.
However, although some studies are of a higher quality than others (as seen on the evidence pyramid), some scientific studies are better at answering specific types of questions.
Etiology:Cohort or case-control study
Harm (Is the intervention being studied harmful?): Cohort study, RCT, or case-control study
For rare diseases, it is actually best to examine case studies, despite their location at the bottom of the evidence pyramid. This is because sometimes a disease is so rare there aren't enough participants for a randomized controlled trial to be conducted.