Newspaper article Pittsburgh Post-Gazette (Pittsburgh, PA)

Measuring Record Crowd Presents Unique Challenge

Newspaper article Pittsburgh Post-Gazette (Pittsburgh, PA)

Measuring Record Crowd Presents Unique Challenge

Article excerpt

An estimated 380,000 people crowded Downtown on Wednesday for the Stanley Cup victory parade.

Or did they?

City officials said the figure stood between 380,000 and 400,000 people, but some news outlets reported more than 400,000 were there. Everyone agreed on one thing, however: It set a record.

"It's the largest crowd we've seen in the city of Pittsburgh," said Guy Costa, city chief operations officer.

Gauging the size of a crowd is an imperfect science. Pittsburgh officials used simple math to estimate and predict the size of Wednesday's crowd. But sometimes the numbers are not what they seem.

"Estimating crowd sizes is a difficult problem, with typical methods producing notoriously unreliable estimates," said Carnegie Mellon University statistics professor Christopher Genovese.

Moving crowds, like those Wednesday, are more difficult to measure and result in more imprecise estimates, Mr. Genovese said. Although Pittsburgh public safety officials relied on sidewalk square footage and crowd density to estimate Wednesday's crowd, Mr. Genovese said looking at a crowd from an angle gives a misleading view of its density.

"Not all photos are created equal," Mr. Genovese added.

Bias also can pose a problem. Mr. Genovese said the parties involved in estimating crowds often have a direct interest in skewing the final count. Research has shown that police estimates tend to be more reliable than estimates from event organizers.

The city used a simpler version of a tried and true method of quickly calculating crowd size. This method begins with the population density of a 10-foot area and then multiplies by the total square footage of the crowd. In densely packed crowds, a single person occupies about 2.5 square feet.

It's easy arithmetic, but it does not always lead to precision.

Wednesday's parade route was 12,000 feet long, with fans standing on the sidewalk 10 to 15 people deep. …

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