So, you think you've honed the Netflix recommendation engine by rating a thousand movies? That's nothing, according to the company's internal statistics.
Several hundred Netflix members have rated more than 50,000 filmed entertainment programs. 50,000! To watch all those at a pace of one movie or TV show per day, it would take 136 years.
But those users are just the extreme end of a broader behavioral pattern. About a tenth of one percent (0.07%) of Netflix users -- more than 10,000 people -- have rated more than 20,000 items. And a full one percent, or nearly 150,000 Netflixers, have rated more than 5,000 movies. By contrast, only 60 percent of Netflix users rate any movies at all, and the typical person only gives out 200 starred grades.
Who are the subset of users who choose to make evaluating movies into an obsession instead of a casual exercise? They are nurturing the Netflix algorithm, training it. But why?
The two biggest raters I was able to track down had each reviewed in the neighborhood of 6,500 programs. Both are long-time users and neither intended to end up putting so much data into the system. But they were aware that there was an algorithm out there awaiting their input to reshape itself to their desires.
Mike Reilly, a producer, has rated more than 6,500 movies. At first, he just rated movies as they showed up, but then he heard about the Netflix Prize, a high-profile competition to improve the accuracy of the service's predictions.
"I became fascinated with the concept, the different approaches people were taking, and the practicality of these applied theories," Reilly told me.
He didn't employ a consistent methodology, rating in spurts and usually while searching for something to watch. What's fascinating is that Reilly noticed changes in the quality of the Netflix predictions as he rated more and more movies.
"The recommendations are better by far [than at the beginning]. I would say that from 0 to about 500 was pretty useless, at 1,000 to 2,000 it got a lot better -- then tailed off to about 5,000. From then on it's been pretty fantastic," he said. "It's really difficult to find something you simply don't know about -- this new system not only finds it, but can really pinpoint why it thinks you'd like it -- there's not just content, but the context as well, and that's really helpful."
That said, even after 6,500 ratings, the system still recommends bad choices occasionally.
"At this point it's just throwing, like, every Star Trek episode at me -- I've never really seen [that program] and am not interested, but it's like 'this is all that's left so we're going to keep asking, oh, and are you sure you still don't want to watch Mystery Science Theater 3000?'" Reilly said. "It's the same with kids movies."
Lorraine Hopping Egan, a book author, has rated 6,471 movies, but feels that the recommendations she gets aren't commensurate with the time she's invested.
"When I first joined, I went into a ratings frenzy because it was fun to say 'I saw that! I loved that! Overrated!' But mostly, I've rated movies as they popped up, in part so that they would stop coming up and I'd see more missed gems," she wrote to me. "But after 10 years, the recommendations are pretty thin and off-track."