Culture: Film lovers need rotten tomatoes

As a one-time film critic who has just co-produced a movie, I'm going to be monitoring the reviews of How to Lose Friends & Alienate People very carefully. I will be particularly anxious about those reviewers whose judgement I respect.

However, I won't attach that much importance to what individual critics say. The only truly reliable guide to a film's quality is the aggregate score of all the critics as recorded on www.rottentomatoes.com. This website – which links to reviews from all over the world – assigns a percentage score to each critic's ranking, with one star being 20 per cent, two stars 40 per cent, etc, and aggregates the total.

The reason this score is more significant is because people are more likely to be right collectively than they are individually. According to James Surowiecki, The New Yorker's financial columnist, a common trick performed by business-school professors is to ask the students in their classes to guess how many jellybeans there are in a jar. Individually, their answers are wildly inaccurate, but an aggregate of all the answers is nearly always within three per cent of the correct number.

We can see the same phenomenon on Who Wants To Be A Millionaire? When contestants use their "Phone a Friend" lifeline, the answer is likely to be right 66 per cent of the time; when they use their "Ask the Audience" lifeline, the answer will be right 90 per cent of the time.

This is not to say that films that make more money at the box office are better than those that don't. After all, whether people go and see a film is dependent on a huge number of factors, only one of which is good word-of-mouth. (The big studios typically buy the opening weekend and then hope for the best.) Rather, the collective opinion of any large group of people who have seen the film is a good index of its quality. Indeed, the aggregate score assigned to films by rottentomatoes.com is similar to the test-screening scores that all film-makers attach huge significance to, no matter how highbrow. In a sense, the verdict of the critics, as recorded by this website, is the final test-screening a film will face.