Economist Paul Samuelson published his theory of revealed preference in the late 1930s. Revealed preference theory basically allows economists to calculate the preferences of a consumer – what that consumer considers his/her best available option in a given situation – using his or her purchasing behavior. Revealed preference theory has been influential to consumer choice theory because it allows economists to get a relative sense of preferences without mapping a consumer’s entire utility function.

This is a big deal because if you want to know what I’m going to like, or if I’ll like thing A more than thing B, you can just look at what I’ve chosen in the past rather than trying to figure out what I think of goods A and B at every price point.

I’ve begun to realize there’s a parallel with consumer web services and the “data exhaust” they generate: namely, that you can use my past behavior on some web services to predict what I will prefer on entirely different web services.

Let’s look at a two-company example of Foursquare and Yipit. Foursquare is a mobile service that allows me to check in to locations I’m at – businesses, parks, airports, offices, etc. – while Yipit is a daily deal aggregator. Like other daily deal sites, Yipit sends me one email each day with a deal they think I’ll find relevant, based on a few things I’ve told them about my preferences. (Screencap below.)

Selections like Yipit’s aren’t ideal: I have to fill them out, which takes time; there’s not the granularity I’d prefer among business types, times, locations (and if there were, there’s a good chance the interface would be complicated); and I have to tell the system explicitly what I want, so my answers will be subject to conscious and unconscious biases.

Suppose I’m interested in discounts on tanning services, but only in January and February, when the weather’s cold, and I feel pale. I could log on to Yipit, select “Tanning” in early January, peruse the deals that hit my inbox, log back on in March, and de-select the Tanning box – but c’mon. That all takes time, and it comes with cognitive load: I have to remember to do it. I have no access to data from Yipit, but I’d bet that preferences users set when they sign up are rarely changed. I believe first choices often become rules, which is why defaults and initial experiences are so important.

Enter Foursquare, which records places I’ve said I’ve been at specific times. If you’re a Foursquare user, log in to the website and check out this page: it’ll give you a preview of what the API spits back as your checkin history. Today, I can retrieve 283 days’ worth of my data, which amounts to 987 checkins at 471 unique locations. For any location, I can pull how often I visit (frequency), when I visit (times/days/months/seasons), and how many other people have checked in (popularity.)

I’d much prefer my Foursquare data power Yipit’s selection algorithm:

1. Foursquare gives more granular data than anything I’d have the patience to enter myself.

2. Foursquare knows where I go and where I don’t, which gives it the ability to target location within a few blocks. Courtesy of Where Do You Go, here’s a snapshot of my New York City checkins. Foursquare knows I spend 95% of my time in New York in the East Village or the Union Square/Flatiron area. I may want restaurant deals, but if Yipit gives me a restaurant deal in Tribeca (or worse, the Upper West Side) I’m never going to take it.

3. Yipit’s deal targeting becomes based on the types of venues I’ve been – and assumedly like – not what I say I like. Targeting drops down to “sushi places in the East Village” or “Italian sit-downs in Soho” rather than “New York City restaurants.”

Foursquare and Yipit represent a base or simple idea of what happens when data (or data exhaust) from one service is routed to another service. There are many, many more interesting things to do here.

At the end of this post – well, I want to say that I know and immensely respect the Yipit team. They’re really smart and dedicated, and they’re thinking of all of these things, plus more. I have no doubt they’re going to be successful.