mathbabe

The gmail filter

If you’re like me, a large part of your life takes place in your gmail account. My gmail address is the only one I use, and I am extremely vigilant about reading emails – probably too much so.

On the flip side, I spend quite a bit of energy removing crap from my gmail. When I have the time and opportunity, and if I receive an unwanted email, I will set a gmail filter instead of just deleting. This is usually in response to mailing lists I get on by buying something online, so it’s not quite spam. For obvious spam I just click on the spam icon and it disappears.

You see, when I check out online to pay for my stuff, I am not incredibly careful about making sure I’m not signing up to be on a mailing list. I just figure I’ll filter anything I don’t want later.

Which brings me to the point. I’ve noticed lately that, more and more often, the filter doesn’t work, at least on the automatic setting. If you open an email you don’t want, you can click on “filter messages like these” and it will automatically fill out a filter form with the “from” email address that is listed.

More and more often, these quasi-spammers are getting around this somehow. I don’t know how they do it, because it’s not as simple as changing their “from” address every time, which would work pretty well. Somehow not even the email I’ve chosen to filter is actually deleted through this process.

I end up having to copy and paste the name of the product into a filter, but this isn’t a perfect solution either, since then if my friend emails me about this product I will automatically delete that genuine email.

The modeling feedback loop

This is a perfect example of the feedback loop of modeling; first there was a model which automatically filled out a filter form, then people in charge of sending out mailing lists for products realized they were being successfully filtered and figured out how to game the model. Now the model doesn’t work anymore.

The worst part of the gaming strategy is how well it works. If everybody uses the filter model, and you are the only person who games it, then you have a tremendous advantage over other marketers. So the incentive for gaming is very high.

Note this feedback loop doesn’t always exist: the stars and planets didn’t move differently just because Newton figured out his laws, and people don’t start writing with poorer penmanship just because we have machine learning algorithms that read envelopes at the post office.

But this feedback loop does seem to be associated with especially destructive models (think rating agency models for MBS’s and CDO’s). In particular, any model which is “gamed” to someone’s advantage probably exhibits something like this. It will work until the modelers strike back with a better model, in an escalation not unlike an arms race (note to ratings agency modelers: unless you choose to not make the model better even when people are clearly gaming it).

As far as I know, there’s nothing we can do about this feedback loop except to be keenly aware of it and be ready for war.