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Case series rarely provide reliable evidence of treatment effects.
However, reports of several patients with a particular health condition sometimes reveal dramatic effects of treatments.
For example, people almost never have spontaneously punctured colons (the lower part of your bowel), so case series that document how many people having colonoscopy (a diagnostic test that involves inserting a tube in the colon) experience a punctured colon can provide a reliable estimate of the effect of colonoscopy on this outcome.
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