We've been talking a lot in lecture about correlation, causation, and how we can really parse these ideas out.  We know that in biological systems, there's a lot we can't manipulate- either there's an ethical, structural or logistical constraint that prevents us from doing a classical controlled trial to establish causality. Luckily, there's a structured approach to evaluate strength of evidence in situations like these, the Bradford Hill Criteria. For this week's discussion, please read Urban pigeons losing toes due to human activities When formulating your discussion, think of a few questions: How do the author's claims hold up to each of the Bradford Hill criteria? What constraints did the authors face when taking these data? Could any of your concerns about causality be resolved by a change to the experimental design? Are the authors conclusions plausible? Are there alternate explanations that seem more reasonable to you? Why?