The New York Times is one of the most popular news destinations on the Internet. Its online audience has been growing steadily for years, but over the first half of 2010 the number of monthly visitors to Times-owned sites surged—from 53 million to 72 million people, according to comScore, one of the leading firms tracking Web usage.

Why the sudden boost? The surge was a methodological anomaly: comScore decided to change the way it counts online users. Both comScore and its biggest rival, Nielsen NetRatings, have been revamping their secret formulas to bring their audience tallies closer to what online media outlets claim. But the two firms don’t often agree with each other, either. In May comScore gave Washingtonpost. com an audience of 17 million “unique visitors,” while Nielsen recorded fewer than 10 million. Their calculations of Yahoo’s audience differed by 34 million people, roughly the population of Canada.