Wednesday, August 14, 2019

Agent-based simulations and horse-race journalism

[This was never my area of expertise, and what little I once knew I've mostly forgotten. Since lots of our regular readers are experts on this sort of things, I welcome criticism but I hope you'll be gentle.]

I tried a little project of my own back in the early 2000s. One of these days, I'd like to revisit the topic here and talk about what I had in mind and how quixotic the whole thing was, but for now there's one aspect of it that has become particularly relevant so here's a very quick overview so I can get to the main point.

Imagine you have an agent-based simulation with a fixed number of iterations and a fixed number of runs. You randomly place the agents on a landscape with multiple dimensions and multiple optima and have them each perform gradient searches. Now we add one wrinkle. Each agent is aware of the position of at least one other agent and will move toward either the highest point in its search radius unless another searcher it is in communication with has a higher position in which case it heads toward that one.

What happens to average height when we add lines of communication to the matrix? At one extreme where each searcher is only in contact with one other, you are much more likely to have one of them find the global optima but most will be left behind. At the other extreme, if everyone is in contact with everyone, there is a far greater chance of converging on a substandard local optima. Every time I ran a set of simulations, I got the same U-shaped curve with the best results coming from a high but not too high level of communication.

It is always dangerous to extend these abstract ideas derived from artificial scenarios to the real world, but there are some fairly obvious conclusions we can draw. What if we think of the primary process in similar terms? Each voter is doing an optimization search, bringing in information on their own and trying to determine the best choice, but at the same time, they are also weighing the opinions of others performing the same search.

Given this framework, what is the optimal level of communication between voters via the polls? At what point does the frequency of polling reach a level where it makes it more likely for voters to converge on a sub-optimal choice? I'm pretty sure we've passed it.

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