Read more from Slate's Summer Movies special issue.
Ideally, studios and exhibitors would just tell us the raw number of tickets sold. Since they don't, Box Office Mojo's inflation-adjusted all-time top 100 list attempts to measure just that—translated into money terms. It takes the film's gross and divides it by the average ticket price in the year the film was released to find total attendance.
It then multiplies that figure by the average ticket price in 2009 to find its gross in today's terms (since it's hard to wrap our minds around a figure like "74 million tickets sold" when we're already trained to think about money).
Box Office Mojo's nonadjusted list is dispiriting: A few Spider-Mans here, a couple of Shrek sequels there. All but two of the top 20 have been released since 1993. But the real list is packed with cultural icons. Rounding out the top five are Star Wars, The Sound of Music, E.T., and The Ten Commandments. The Graduate, the anthem of a generation, is stuck down at 380 when you ignore inflation but rises to 18 when you don't. Snow White and the Seven Dwarfs is 108 on the nonadjusted list, trounced by every Pixar movie except A Bug's Life. Adjust for price increases, and it passes them all, to no. 10.
Box Office Mojo's method is far from exact, as the site's president, Brandon Gray, confessed in a recent conversation. Box office data from before the 1970s are spotty, requiring some Hollywood archaeology to piece together estimates. The site's dependence on average ticket price is also problematic. Certain movies sell a higher proportion of children's tickets (which are discounted) or do better in big cities (where tickets are pricier). In the old days, big-event roadshow movies like The Sound of Music would cost more than other films. Plus, the site doesn't recognize that the cost of a movie ticket has risen faster than the consumer price index. In other words, a ticket to Up in 2009 is more expensive in relation to other items people can buy than a ticket to Gone With the Wind was in 1939.
Population growth is another complication. If our measurement is the number of tickets sold, isn't Gone With the Wind at a disadvantage as compared with TheDark Knight because there were fewer than half as many people in the United States in 1939 than there are now? Should our measurement be the very unsexy "number of tickets sold per 100,000 people"?
Exactitude is impossible, but a simple acknowledgement of basic economics would be a giant leap forward. So this summer, let's all strive for accuracy when discussing box office feats. (That goes for you, too, Broadway, and your suspect use of the term "house record.") Journalists who don't think they have time to care about price increases can subscribe to Box Office Mojo's paid service that adjusts most charts for you. And readers, in turn, should refuse to listen to statistics that lie. That way, when the next Gone With the Wind comes along, we'll know how to recognize it.