In the last few years I have been a rather loyal Netflix user. Their streaming selection is weak, but their DVD mail service is very convenient. One thing strikes me as odd though: their celebrated movie recommendations—based on collaborative filtering—are typically worthless. Most recently I was trying to figure out their three star prediction for Prometheus, which in my humble opinion is really the slime at the bottom of the Hollywood barrel. And then it occurred to me: maybe it’s my younger self’s fault?
When I’m asked to rate a silly movie like Indiana Jones or Terminator, which I haven’t seen in a very long time, I get nostalgic. As a kid I used to love these movies, but as a kid I also thought the funniest joke in the world was this thing (admittedly it’s a bit funnier in Hebrew). My rating for those movies is based on fond and distant memories, which may not be consistent with my adult point of view. Is this what Netflix “wants me to do”? This is perhaps the wrong question to ask; the right question is, how would another person with a similar taste profile rate one of these silly movies that we both loved as kids but haven’t watched since?
To make things more complicated, consider this. I’m in my early thirties, so as a kid I watched movies that were released in the late eighties and early nineties. In contrast, as a kid I don’t remember watching any movies that came out, say, in the fifties; I evaluate these movies based on my adult taste. Now, someone who is his sixties could have identical taste to mine, but may evaluate fifties movies based on his childhood taste and eighties movies based on his adult taste.
Ever the diligent scientist, I sampled Netflix’s rating queries (“rate what you’ve seen to discover suggestions for you”). Among twenty that were displayed, four (20%) fall into the problematic category of “movies that I watched as a kid but haven’t seen since”: Three Men and a Little Lady, Parenthood, Under Siege (Steven Seagal exterminates bad guys), and Sneakers (which actually falls into the more embarrassing subcategory of “movies that I watched in the cinema with my mom”). I would love to see the results of the following experiment: take people’s ratings and restrict them to movies that they watched in the last five years; would that make Netflix’s disappointing predictions more or less (in)accurate? It’s hard to predict (no pun intended). Yep, research was like a box of chocolates: you never know what you’re gonna get.