When activists stage an event, they want to impress others with their commitment, unity, their worthiness, and their numbers.  (This formulation is from the great sociologist, Charles Tilly.)

They want to show their opponents that they are strong and powerful–and not going to go away.  They want to show their allies in government that there are enough of them to deliver the rewards politicians care about–votes and campaign support, for example.  They want to show potential supporters that they are worthy: perhaps that they are regular folk just like those watching; perhaps that they are particularly well-informed.

In general, the more dramatic and disruptive the action, the fewer people you need to make an impact.  But the large demonstration on the mall in Washington, DC* is such a staple of American politics that large numbers matter.

Glenn Beck joked at the August 28th “Restoring Honor” rally that he had “…just gotten word from the media that there is over 1,000 people here today.”  Later, he offered estimates of 300-500,000 attendees.  Mass media reports were all over the place, from CBS’s estimate of 87,000 up to a few hundred thousand in other mainstream sources, including The New York Times and NBC News.

CBS published photographs showing large areas of open space:

But how do you know?  Activists routinely inflate their best estimates of crowd size.  Sometimes, it’s wishful thinking; often, they anticipate that police or media will deliberately low ball the count.  Certainly you can’t take their word on it.  The most earnest and intrepid reporter on the ground is poorly positioned to count into four or more digits (not a skill routinely developed in journalism school).

Crowd experts get photos from above and count.  They cut the field into grids, count some of them, multiply, and offer something of a fact-based estimate.  CBS actually paid consultants to take aerial pictures and count. Here’s an example they posted:

Of course, this isn’t incredibly precise.  People come and go at large rallies, particularly longer ones, and they may be huddling together to hear a speech, dancing, or sitting on lawn chairs.  Do high school and college students take up less space than older, uh, more substantial (?) people?

In Washington that weekend, I was struck by how many people I saw carrying folding lawn chairs.  Here’s a photo from CNN

I can’t remember seeing so many chairs at any demonstration I’ve attended in the past.  Maybe it’s the crowd, or maybe, as sociologist Bob Edwards suggests, it’s better lawn chairs.

You can count buses or hotel rooms.  Indeed, a hotel clerk in Washington, DC told me that the entire city was sold out for the Friday before the rally, and hoteliers were honoring the demand by charging exceptionally high rates.  But some crowds are more likely to camp out on friends’ floors and pack the hotel rooms than others.  I’d expect that younger (poorer) people are more likely to take the overnight bus from New York or Boston than to come in the night before.

The National Parks Service used to provide the estimate mainstream media quoted, but stopped doing so in 1996 in the controversy about the (maybe not exactly) Million Man March the previous year.  Now, mainstream sources generally report broad ranges (even of hundreds of thousands) or competing claims.  And readers and viewers seem to accept the estimates of the people they like.

Steven Doig, a journalism professor who consulted for CBS, explains the methods and the controversies on his blog.  The basic story is that people who stage the event are unhappy and untrusting when he finds fewer people than they announced.

Meanwhile, Minnesota Republican Michele Bachmann–who was there–announced afterward that “We’re not going to let anyone get away with saying there were less than a million here today – because we were witnesses.”

Alas, such witness testimony tends to be based on faith, rather than fact–not always a big problem for the committed.

* See historian Lucy Barber’s wonderful book, Marching on Washington: The Forging of an American Tradition (University of California Press, 2004)