Wednesday, August 1, 2007

Members Similar To You

The question has been raised: "How are these people chosen?" and "Why do some of my Friends have higher sim% than these people?"

The calculation to determine similarity is extremely complex -- and takes into consideration all the movies you've seen and rated, and how other people rate those movies to find weight, and then looks at the various kinds of overlaps with another person. To take you and compare you to every other subscriber would be CPU prohibitive. To compare you to every reviewer is slightly easier, but still takes many minutes. We use this complex algorithm for you and your Friends since you only have a (relatively) few Friends. But with the larger Community we had to simplify the calculation a little. It's simply not quite as refined as the variation we use on your Friends. The result is that, for the moment, a "very similar" stranger is in going to be in the 70-80% range (i've not seen a 90+ yet) and that's about 10 points below what I get with my most similar Friends. We will continue improving the speed and accuracy of the similarity calculations.

The block of four selected here is not necessarily the four "most similar" people to you. We use a number of quick assumptions to narrow down the field of reviewers we will compare you to, then run the faster similarity calculation on them, and finally randomly select four from the group at the top. This way, it will change a bit from time to time. If we find that people like this block, and enjoy exploring people who are similar, we will expand this kind of feature (maybe get a whole page of similar people, or be able to search for folks, or other interesting things); but first I'd like to see if a lot of folks are intrigued. (And as we know from blog comments here -- a lot of you simply don't care about strangers, so it is most certainly not assured to be a valuable feature). But we're listening. Whatcha think?