Can an interviewer require applicants complete a problem solving case as part of the interview process? If so, does this case need to be the same for all potential applicants?

Some banks require potential lenders evaluate a mock loan and determine whether funds should be lent.

Yes you can as long as you use the same problem or processes with all applicants interviewed for the same position.

I was waiting until someone with subject matter expertise weighed in before I offered a layman's observation: Every interview is a "case study" and there is never a guarantee they will be homogeneous. Interviewees for a technical position should be grateful for the possibility that they would be offered a question more relevant than, "How would you describe yourself? or "Where do you want to be in 10 years?"

If you can develop a good vignette or a choice of three to offer a candidate it will be no small task. It will also be incumbent on the interviewer to have some sort of a clue as to whether the answer is accurate and insightful. The technique raises the bar on both sides of the desk.

Is "testing" a underwriter on how to underwrite a loan any different than testing a secretary on how many words they type a minute. I agree w/ Ken - I'd much rather be asked about something I know. And I tend to ask questions as such when interviewing.

A side note - A personal pet peeve of mine in an interview is when someone tells me they're "self motivated". I then ask them to discribe how they are self motivated and what techniques they would use in the position they are applying for.

One thing to be careful about in an interview is a perception of bias. If you come up with three questions, you can't pick and choose which each candidate will get. Letting them choose might be OK, but it's a gray area. If a candidate does claim bias later, how do you prove that you didn't somehow direct them to a harder question than the candidate that you hired through tone or inflection?

Sadly, most interviewers ask those same bland little pre-approved questions in all interviews such as "How would you describe yourself" because there is such a chance of lawsuit if they instead ask on candidate "What would you describe as your best qualities?" since this may allow other candidates to give descriptions that may seem more negative and thus show bias toward that one candidate.