They used statistics to crunch the numbers, and they found out that name actors can contribute to a film's financial success. So can crowd reviews.
20% is still unexplained. Is that a big issue in statistics? I don't know.
Taken together, these factors explain about 60% of the variation in box-office revenues. Adding an estimate of marketing costs increases our model’s accuracy by another 20 percentage points. That leaves about one-fifth down to factors not explained by the model. “John Carter”, a $275m science-fiction extravaganza that was one of the biggest turkeys in Hollywood history, should have earned $235m according to our model. It made just $73m when it was released in 2012. Clearly, no one yet knows everything.
20% is still unexplained. Is that a big issue in statistics? I don't know.