Prediction with Multilevel Regression Models, and Pizza

October 15, 2010
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(This article was first published on Somethink to Chew On » R, and kindly contributed to R-bloggers)

The Meetup phenomenon, which is now substantial and longstanding enough to be more of a cultural change than a flash in the pan, continues to impress me. Even more so than tools like LinkedIn, Meetups have changed the nature of professional networking, making it more informal, diverse, and decentralized. Last night, statistics consultant (and cheap eats guru) Jared Lander and I presented a talk on a statistical technique tangentially related to my professional work (more closely associated with Jared’s). The origin of this presentation is worth noting. On Meetup’s web site, members of a group can suggest topics for meetings. Before even attending a single NYC Predictive Analytics event, I posted several topics that I thought might be interesting for the group. A bit later, the organizers (Bruno and Alex) contacted me to see if I’d be willing to present on prediction with Multilevel models. I said that I would, but only if I could co-present with someone who actually knew something about the topic a complementary set of skills and experiences. Knowing Jared from the NYC R Meetup group, and knowing that he learned about multilevel models from the professor who wrote the best book on the topic, and knowing that he’s pretty good in front of an audience, I suggested we collaborate.

Despite requiring a lot of work, and a lot of learning of details on my part, we managed to throw together a pretty decent talk. (As of this morning, there’s four ratings of the event on Meetup, and we got 5/5 stars! Yay us! Not statistically conclusive, though…) We used as an example topic for data analysis the difficult and critically important problem of predicting reviews of pizza restaurants in downtown NYC. Jared is actually an expert on this topic, having written his Masters thesis on ratings from Menupages.com. For the talk, Jared would present a few slides, then I’d present a few. In a few cases we’d both try to explain topics from slightly different points of view. I’d repeatedly try to use the keyboard instead of the remote-control gadget to control Powerpoint, causing the computer to melt down into a pile of slag and refuse to change the slide. Jared would send me withering glares when I started to move towards the keyboard. It ended up OK, though, we got through everything, and even answered about half of the (excellent) questions! Oh, and shout-out to the AV guy at AOL HQ. I don’t know how they pay his salary, but he rocked.

Jared has posted the slides from the talk here (ppt), and I’ve put the data we made up (for pedagogical purposes) and the code we used to analyze it and generate graphs for the talk here on Github. Alex video-recorded the presentation, and I’ll update this sentence to link to the video once it’s posted somewhere. Hope folks find it valuable!

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