Classroom Activity: When Silence Says a Lot

23 April 2014, 1602 EDT

This activity comes after students are to have listened to a lecture (slides) on international institutions, specifically the impact they have on patterns of armed conflict. The first half focused on peacekeeping, which works better (under some conditions) than many appreciate, while the latter focused on how international institutions can deter bad behavior even if they lack enforcement power. The argument, which I previously laid out (in a somewhat different form) here, is that international institutions need not have the power to punish so long as the statements they make have an impact on the likelihood that someone else will do so.

If institutions issue reports condemning bad behavior, which they don’t always catch, but never go out of their way to praise good behavior, then one might think that they only influence beliefs when they issue reports. But that’s not correct, at least if governments are even weakly Bayesian. Every time a report is not issued about a given state violating international law or otherwise misbehaving, a little more information is revealed.

To illustrate this somewhat subtle point in a light-hearted manner, I devised the following activity.

I wasn’t looking for a precise probability. I’d need to provide more information than I did for that to be possible. All I asked them to do was tell me whether they’d still think there was a 50% chance that the movie would stink, or whether they’d revise that number up or down.

The correct answer, which many of them identified, is that you should now believe there is less than a 50% chance that the movie will stink. (As you’d expect, most of those who got it wrong failed to update their beliefs. What I didn’t anticipate is that a few of them become more convinced that the movie would stink.) There are lots of reasons why the blog might not have posted a review, and I told them that they should assume they see at least one movie a year that they end up hating which nonetheless escaped the wrath of this hypothetical ultra-snarky blog, but the absence of a scathing review should at least modestly decrease your fear that the movie will stink.