[arafa]

But is there data to support that these questions are effective in finding the types of people that you want? Without concrete and consistent answers to questions, you'll be exposing yourself to bias (subconsciously encouraging people like yourself or seeing their vague answers in a more positive light). You'll also make more of the interviewing experience dependent on what you happen to think of and the mood you're in at the time, increasing the inconsistency of your interviews.

I know the intuitive idea is that you'll get to see how the candidate reacts, but that can be done in a less arbitrary way (and in a job-dependent context) through behavioral interviews and the like. Brain teasers are also often poor candidate experience, since they can feel unfair and unrelated to the work. If estimation is a key feature for PMs, it should be part of the interview process with well-defined procedures.