> (From the article) Our brains reason better with causes, rather than with numbers. In variation B, the idea that Ones are more prone to the disease is a cause

> (From the article) Our brains reason better with causes, rather than with numbers. In variation B, the idea that Ones are more prone to the disease is a cause we can latch on to, and it helps us discount the results of the ethnicity test as we should. The fact that variations A and B both have the same answer means that the likelihood of Ones having the disease is irrelevant to the problem statement. It's really funny that "Ones are more prone to the disease" in variation B is supposed to help us intuit the correct conclusion when it's not actually relevant information. Writing the math out shows that P(disease=True) does indeed drop out of the P(identity=Two | disease=True, ethnicity-test=Two) calculation. Edit: Adjust quote formatting.