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.

Parts of that argument are unfair. People voting on new movies often haven't seen the old ones, but obviously most people who voted on the old ones haven't seen the new ones, either. I'm not sure whether "see how it dates" is a good criterion either -- it's basically saying that what we think of as good movies changes over time, which isn't ever an argument against any particular movie. If we want to keep the ratings more modern, we could weight new votes more than old votes.

If IMDB exists 100 years from now, it will probably at least be effective at comparing non-recent movies from different time ranges. The two movies that got compared would get a chance both at the new-fan vote and the old-fan vote. Assuming value drift, it's not clear that the comparison would be meaningful, but it would at least be fair.

I don't think it's obvious that people voting on old movies haven't seen new movies.

It might be likely that people who watch many old movies are less likely to have seen new movies, but it could just be that these people watch more movies in general.

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Simple theory of IMDB bias

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Simple theory of IMDB bias

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