Joel On Interviewing 12: The Design Question
Ask the candidate to design something. Jabe Blumenthal, the original designer of Excel, liked to ask candidates to design a house. According to Jabe, he's had candidates who would go up to the whiteboard and immediately draw a square. A square! These were immediate No Hires. In design questions, what are you looking for?
Good candidates will try to get more information out of you about the problem. Who is the house for? I will not hire someone who leaps into the design without asking more about who it's for. Often I am so annoyed that I will give them a hard time by interrupting them in the middle and saying, "actually, you forgot to ask this, but this is a house for a family of 48-foot tall blind giraffes."
Not-so-smart candidates think that design is like painting: you get a blank slate, and you can do whatever you want. Smart candidates understand that design is a difficult series of trade-offs. A great design question: design a trash can for a city street corner. Think of all the trade offs! It has to be easy to empty, but impossible to steal; it has to be easy to put things into, but hard for things to fly out of on a windy day; it has to be solid, yet inexpensive; in some cities, it has to be specially designed so that terrorists can't hide a bomb in it.
Creative candidates will often surprise you with an interesting, non-obvious answer. One of my favorite questions is Design a Spice Rack for Blind People. Inevitably, candidates will put Braille somewhere on the spice bottles, and it usually winds up being on top of the lid for various reasons which you'll discover after you've asked this question 100 times.
I had one candidate who decided that it would be better to put the spices in a drawer, because it is more comfortable to scan Braille with your fingertips horizontal than vertical. This was so creative it surprised me -- in dozens of interviews, I had never heard that answer. And it really took a major creative leap outside of the bounds of the problem. On the strength of that answer alone, and no negatives, I hired the candidate, who went on to be one of the best program managers on the Excel team.
Look for closure. This is part of Get Things Done. Sometimes candidates will drift back and forth, unable to make a decision, or they will try to avoid hard questions. Sometimes they will leave difficult decisions unanswered and try to move on. Not good.
Good candidates have a tendency to try to naturally keep things moving forward, even when you try to hold them back. If the conversation ever starts going around in circles, and the candidate says something like "well, we can talk about this all day, but we've got to do something, so let's go with decision X" that's a really good sign.