Simple theory of IMDB bias

taw

IMDB top 250 list is dominated by old movies, which conflicts with my perception (shared by majority of people as far as I can tell) that new movies are far better than old movies (comparing either top with top or average with average).

I have a simple theory why IMDB is wrong:

For new movies, very wide population have seen it, many not fans of the genre. They vote on IMDB soon after watching.
For old movies, only narrow population of fans have seen it recently. The only people who vote on IMDB are those who've seen it recently (atypical fans), or have particularly good memories of it (atypical fans again). People who watched an old movie ages ago but don't remember much about it are very unlikely to vote on IMDB.
Therefore it's much more difficult for a new movie to get a good IMDB score than it is for an old movie.
Therefore a new movie with identical IMDB store is likely much better than an old movie with identical score.

The "correct" procedure would of course be gathering random sample of people, showing them random movies, and asking for ratings just after the movie. For practical reasons this cannot really be done, so the next best thing we can do is ignoring old movies with unreasonably high IMDB scores.

I have a simple theory why IMDB is wrong:

For new movies, very wide population have seen it, many not fans of the genre. They vote on IMDB soon after watching.
For old movies, only narrow population of fans have seen it recently. The only people who vote on IMDB are those who've seen it recently (atypical fans), or have particularly good memories of it (atypical fans again). People who watched an old movie ages ago but don't remember much about it are very unlikely to vote on IMDB.
Therefore it's much more difficult for a new movie to get a good IMDB score than it is for an old movie.
Therefore a new movie with identical IMDB store is likely much better than an old movie with identical score.

It's obvious not because of any character trait that those people have, but because the majority of the voting on those movies was done before the new movies came out.

I was going to say that this is likely more true for movies coming out in 2011 than 2000, which I still believe somewhat, but cursory research indicates that imdb was started in 1990 and acquired by amazon in 1998, so even in the year 2000 imdb was fairly large, and therefore probably had reasonable traffic.

When I thought about older movies I thought about movies from the '50s and '60s especially, where all of the reviews necessarily came out long before the movies were released, rather than movies from the '90s, where the effect you mention should be pretty strong.

So my new hypothesis in your vein would be that '90s movies should be over-represented compared with '00s movies.

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Simple theory of IMDB bias

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Simple theory of IMDB bias

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