## Wednesday, June 29, 2011

### The problem with "puzzle" interview questions: I - The what

I like puzzles. I solve them for fun; I don't like when companies use them for recruiting, though.

Some companies use puzzle-like questions as interview devices for knowledge workers. Other than the obvious inefficiency of using proxies when there are direct measures of performance, many of these questions penalize creativity and thinking outside the box defined by the people who are conducting the interview (usually the potential coworkers).

Here's a thought: if hiring a programmer, ask a programming question. For example, give the interviewee a snippet of code and ask what its function is; ask how it could be optimized; ask what would happen with some change to the code or how a bug in a standard subroutine would affect the robustness of the code.

Here's a second though: if hiring statisticians, instead of trying to trip them with probability puzzles (especially when your answer might be wrong), show them a data-intensive paper and ask them to explain the results, or to consider alternative statistical techniques, or to point out limitations of the techniques used. Perhaps even -- oh what a novel idea -- consider asking them to help with an actual problem that you're actually trying to solve.

My job interviews, in academe, were like these thoughts: I was asked, reasonably enough, about my training, my research, my teaching, and to demonstrate the ability to present technical material and answer audience questions; job-related skills, all, even though some interviewers were interested in puzzles.

In social events, however, some acquaintances have asked me questions from interviews; here are a couple of responses one could give that are correct but unacceptable to most interviewers:

How would you move Mount Fuji?

Well, in a universe in which the Japanese people and government would allow me to play around with one of their most important landmarks, I'd probably be too busy simuldating Olivia Wilde and Milla Jovovich to dabble in minor construction projects. But if I had to, I'd use a location-to-location transport beam from my starship, the USS HedgeFund.

Or did you want to know whether I can come up with the formula for the volume of a truncated cone?

What is the next number in this sequence: 2, 3, 5, 7, 11,...

It's pi-cubed. You are enumerating in increasing order the zeros of the following polynomial
$(x - 2) (x - 3) (x - 5) (x- 7) (x - 11) ( x - \pi^3).$
Or did you think that there was only one sequence starting with the first five prime numbers?

Bob has two children, one is a boy. What is the probability that the other is a boy?

I made a video about that. (Even after that video, or my live explanation, some people insist on the wrong answer, 1/3; proof that there are few things more damaging than a little knowledge matched with a big insecure ego.)

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I'll have a later post explaining the deeper problem with using puzzles (and its dynamics), part II of this.