*Clears threat*. Did anyone perhaps inquire about Bayesianism? See, it can be explained by Bayes theorem. P(A | B) = P(B | A) * P(A) / P(B) Look at all orde

*Clears threat*. Did anyone perhaps inquire about Bayesianism? See, it can be explained by Bayes theorem. P(A | B) = P(B | A) * P(A) / P(B) Look at all ordered pairs of people in a couple. Let A be the proposition that the first person is a Dev, and B be the proposition that that the second person is QA. P(A | B) now expresses how common it is for QA people to have a Dev partner. And P(B | A) expresses how common it is for devs to have a QA partner. What the theorem tells us that the difference is simply explained by P(A) / P(B), that is the relative commonness of the professions. Or to be precise the commonness of the professions in the subset of people who have a partner.