Tag Archives: Probability

The social contract at coffee shops

Miscellaneous, , ,

Coffee cupA friend and I were just taking a coffee break from working at the Sciences Po library, and we started discussing a question that has bugged me in some form for awhile now but which I’d never taken the time to really think through. Here’s the scenario: you’re sitting at a coffee shop or library or a comparable public place to do work on your laptop. You need to use the bathroom or take a 10-minute smoking break outside. Is it safer to just leave your stuff and hope no one takes it, or is it instead a better idea to ask someone specifically to watch your things while you’re away?

Most people will choose the second option. But I’m not convinced this makes sense. The way I see it, this is a mathematical problem with two potential variables: aggregate probability of any random person in the vicinity (either inside the coffee shop/library or nearby) stealing your laptop, and probability of the person you specifically told to watch your stuff stealing your laptop. So in the first scenario, if you don’t tell anyone you’re leaving, a good portion of the people in the shop may not even know for sure where you went, how long you’ll be gone, if you came in with the person who happens to be sitting next to you, etc. Thus, the probability of something being stolen is pretty low by default.

On the other hand, telling someone to watch your stuff should (theoretically) reduce the probability of anyone else stealing your things to almost zero. However, that person now knows for sure that you have gone somewhere and plan to be away for at least several minutes, so the probability that (s)he will take your things seems — to me, at least — to be decently higher (relatively speaking, of course; obviously, the average person you ask to watch your stuff is not going to steal it).

Granted, there are a ton of variables that I haven’t brought up. First of all, where are you: an on-campus library at a well-guarded university with high tuition fees, or a Starbucks in Detroit? Secondly, are you asking whoever randomly happens to be nearby to watch your stuff, or are you choosing a person based on some characteristics (s)he seems to display? It’s possible that, in the latter case, selection bias could play a large role because (as my friend pointed out to me) most people are likely to choose an innocent, nice-looking person to ask. However, this very person is considerably less likely to actually be willing or able to stop someone from simply grabbing your stuff and walking out. On the other hand, if you ask someone who looks gruffer or more fierce, you have perhaps chosen someone with at least a slightly higher probability of committing theft him/herself. (This is a particularly flimsy assumption, but it’s a possibility worth considering, I think.) There are many more questions too, including whether the very act of asking someone to watch your stuff opens some kind of implicit social contract, but I am very doubtful that this works with someone who was already thinking of stealing your things to begin with.

I always used to think asking someone other than an employee of the coffee shop or library to watch your things was counterproductive, but I’ve seen so many people do it that now I’ve adopted the habit myself. I’d be curious to see some kind of study on this. In the meantime, I found someone who asked the same question and got a bunch of responses.

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