Fulbright in Portugal

Steve Doig in Lisbon August-December 2010

Lisbon skyline

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Another march!

I had yet another chance to do crowd-estimating today. Lisbon hosted the NATO conference here Friday and today, an event that brought out many protesters. Working again with several of my students and my colleague Antonio Granado, we came up with an estimate of the size of the main protest march  that occured this afternoon.

As is the custom for such demonstrations in Lisbon, the protesters gathered at the Marques de Pombal circle, then marched down Avenida da Liberdade to Restauradores.

To estimate this crowd, we had to rely on counting the marchers as they passed by along the avenida. Our protocol was to count how many marchers passed by during 30-second periods, and taking these counts every two minutes. The reason for the protocol is to make sure that the counts were a random selection of the varying numbers of people who passed by; as happens with these marches, sometimes there are large clumps and sometimes gaps or only a few people going past. By using a rigid protocol like this, we avoid unconsciously influencing the numbers by taking counts only when dense or sparse groups were going by.

The front of the march reached my position at 3:55pm and the last of them passed at 4:40pm; thus, the march lasted 45 minutes. My 30-second counts ranged from as high as 300 at the very front of the march to as low as 10 persons during another spot. (No, I didn’t count to 300 for that first one. In fact, I counted about 150 during a 15-second period instead, a necessary fallback when a crowd is very dense. But all the other counts were made during 30-second periods.)

When the march ended, I took the average of the counts (about 68) and then multiplied by two to turn it into average marchers per minute. That answer was 135. I multiplied that by the 45 minutes of the march and got 6,750, which I rounded up to 7,000. I then added an arbitrary 1,000 to account (somewhat liberally) for marchers who may have left before arriving at Restauradores.

My estimate of 8,000 is well below the march organizers’ claim of 30,000 protesters. But there are reasons why the 30,000 claim is not credible.

One reason is this picture taken of the crowd by Antonio from above Restauradores after the last of the marchers reached the plaza.

The area filled by the crowd is about 5,000 square meters. A crowd with this density takes up about 0.7 square meters per person; in this case, that means the crowd area would hold about 7,000 people — not 30,000.

Those who believe the count of 30,000 is accurate cite the fact that the marchers extended the entire length of Avenida da Liberdade; as the front of the march reached Restauradores the last of the march was just leaving Marques do Pombal.

But Avenida da Liberdade is 1,100 meters long, and the street area used by the marchers is 20 meters wide. Therefore the rectangle which contained the march is 22,000 square meters. If every one of the marchers were tight enough to reach out and touch the person in front or next to them, they would use about one square meter per person. Thus it’s possible to have just over 20,000 marchers in Avenida da Liberdade at one time. But this march was not that packed together; as noted above, there were tight clumps and there were empty stretches.

So 30,000 is not credible. For the reasons cited above, I believe that an estimate of about 8,000 is realistic.

(POSTSCRIPT: Some will note that today’s crowd clearly was larger than the trade union march and rally of Nov. 6, and yet I estimated 8,000-10,000 at that event. I have to admit now that I was being overly generous in that earlier estimate. The crowd picture taken then showed maybe 4,000 people, and I doubled that estimate in order to account — way too much, I now believe– for those who wandered away before the march ended. All of which goes to show the importance of being not only realistic in these estimates, but consistent!)

Head-counting in Lisbon

I got a chance to do journalism here in Lisbon today. The Frente Comum de Sindicatos (Joint Trade Union Front) had organized a rally of government workers for Saturday afternoon. The rally was to protest planned cutbacks in salaries and benefits of public employees as part of austerity moves designed to bring Portugal’s budget into better balance. Not surprisingly, public employees complain that they are being asked to make the most sacrifices, and so the rally was designed as a show of solidarity in advance of a countrywide general strike planned for Nov. 24.

In my class at UNL on Thursday, we discussed crowd counting and particularly the obligation of journalists to do independent estimates of the size of political rallies. The problem with such rallies, of course, is that the organizers and the opponents often make wildly inflated or deflated claims about the size of the crowd. Knowing that the rally would be happening today, we decided to see if we could produce such an independent count of the size of the crowd. We did: The answer is below.

To do this estimate, student volunteers stationed themselves along the march route, which was down the 1.1 kilometer length of Avenida de Liberdade. It went from Marques de Pombal plaza where the marchers gathered in advance to Restauradores plaza for the rally at the end. The students gathered information about how many marchers were passing during various short time periods, like 30 seconds, and also how long it took the whole march to pass by. (See results below.)

At Restauradores, my UNL colleague Prof. Antonio Granado talked his way into an excellent vantage point above the plaza, a high window in a building overlooking the whole square. In advance, I had measured the area of the plaza in square meters, information that tells us how many people possibly could fit in the square under various densities.

The march began about 3:30, and the last marchers reached the plaza about 5:15. They marched VERY slowly. When the crowd finally gathered, Antonio took some detailed photos showing the extent and density of the protesters who gathered to hear the speeches from the stage that had been erected in advance.

Between Antonio’s photos and the ground-level observations from myself and the students, I estimated that perhaps 8,000 to 10,000 union members had participated in the march, and that about 5,000 of them had gathered in the Restauradores plaza to hear the speeches.

This estimate is well below the claims that some organizers were making about how many would take part — as many as 100,000 or more. That’s the problem with wildly over-estimating attendance in advance; reality-based counts can make it seem like an event was a failure.

In reality, the area in which the rally took place at Restauradores is about 5,000 square feet in size. A loose crowd in which everyone is arm’s length from those around them, a crowd in which it’s possible to move around without squeezing past others, needs about one square meter per person. As Antonio’s pictures and my ground-level observations show, this was a loose crowd. Therefore, the actual gathered crowd was no more than about 5,000 protesters. The estimate of perhaps 10,000 in the march makes the quite-generous assumption that as many as half of the marchers didn’t stay for the rally.

It will be interesting to see if some of the news media outlets in Lisbon and around Portugal pay attention to our estimate or just accept the inflated claims that will be made.

UPDATE: For those who insist our estimate of no more than 10,000 is way too low, consider this. One of my students, Eudora Ribeira , took very careful counts of the marchers during 30-second periods as they passed by her position on Ave. Liberdade. Her counts of marchers passing in those 30-second periods were 51, 40, 75, 52, 45, 20, 70, 52, 58, 70, 51, 49, 46, 28, 17 and 25. The average of those counts is 94 marchers passing per minute. The front of the march reached her at 16:02 and the last marchers passed her at 17:05, a total of 63 minutes. If you multiply 94 marchers per minute by 63, you get a total of 5,922 marchers, or a rounded figure of approximately 6,000. Another student on Ave. Liberdade, Rita Oliveira, also used the same passing-marchers method, and came up with a march estimate that was somewhat lower. By either method we used — counting marchers or measuring the rally crowd area — you can see the crowd could not have been larger than 10,000.

UPDATE: The newspaper Publico posted a long story from the LUSA wire service. Television also is interested. I was interviewed by the SIC (video here at the 8:00-minute mark) and TVI (video here at the 14:30 mark) news stations. And TV station RTP posted a brief version of the LUSA story about our count.

More head-counting!

FURTHER UPDATE: You can see some great aerial images of the rally on this Photosynth.com page. These are the aerial images produced by the AirPhotosLive.com crew that we used for estimating size of the rally crowd. And for those who want to compare rallies, here are images from the Glenn Beck “Restoring Honor” rally on the National Mall on August 28.

UPDATE: CBS News released our estimate of the crowd at the Stewart/Colbert rally: 215,000 people. See the CBS story and two aerial pictures. More aerial shots will be released soon.

Several readers have asked if I will be involved in estimating the crowd that turned out Saturday for the Jon Stewart/Steve Colbert “Rally to Restore Sanity and/or Fear” in Washington, DC. The answer is yes; once again, I’m working with the AirphotosLive.com crew, as I did with the Glenn Beck rally in August. See this post and this one for descriptions of my methodology for the Beck rally.

We’re getting the aerial images and doing the crowd estimates for CBS News so I can’t release my estimate yet. But I’ll discuss it in the next day or so when the images are released to the public. So watch this space!

Crowd counting (wrapup)

I was amazed and fascinated by all the attention (positive and otherwise) received by my part in estimating for CBS News the size of the crowd at Glenn Beck’s rally Saturday in Washington. My post on that is here. Many have asked to see the Airphotoslive.com images we used in making those estimates. CBS News, which paid for the images, has done a story about the process we used. And many of you will be interested to examine the images in more detail now that CBS News has released them.

To answer a common question for a final time, the images were shot around noon, at the height of the rally. To those of you who were there and believe that the entire crowd area was as packed as wherever you were standing, please note the patches of green and even wide-open areas in parts of the crowd area.

I have spent much of the past three days moderating the many comments I received and trying to answer questions. But I am here in Lisbon to do other things, so it’s time for me to move on. Feel free, of course, to continue to debate this out in the blogosphere; I’m closing out the discussion here. Thanks again for your interest.

[UPDATE: NPR’s “On the Media” program did a nice 8-minute segment Saturday, September 4, on the difficulties of crowd-counting. And here’s a smart op-ed piece that ran in the Los Angeles Times on September 7, written by internationally-known ASU scientist Lawrence Krauss. And in early October I was interviewed about crowd counting by France Info, the country’s national public radio network; their story is here.]

Counting heads

It’s not all porto and pastéis de nata for me here in Portugal. I spent yesterday doing journalism.

I was contacted a couple of days earlier by Curt Westergard, whose Airphotoslive.com company uses cameras on tethered balloons to produce high-resolution aerial photos. He had been hired by CBS News to get images of the crowd that gathered Saturday for the Glenn Beck “Restoring Honor” Tea Party rally at the Lincoln Memorial in Washington. CBS also wanted a credible estimate of the size of the crowd. That’s where I came in.

I started doing crowd estimates back in my Miami Herald days, for local events such as a visit by Pope John Paul II or the annual Calle Ocho street festival. After the 2008 presidential election, I wrote a piece about crowd counting for MSNBC.com, and that led to news media requests for an estimate of the crowd for President Obama’s inauguration. I used a satellite image taken over the National Mall on January 20, 2009, to estimate the crowd there at about 800,000.

Crowd counting, particularly of political events, always is controversial. The organizers of the event inevitably hype their crowd estimate — often grossly — to demonstrate the popularity of their cause, and opponents inevitably underestimate to fit their own agenda. Because of the wild pre-inauguration predictions of how many would attend in person — up to 5 million! — my reality-based estimate was ignored by many left-wing commentators and embraced by those on the right.

Naturally, I expected more of the same about my Beck rally estimate. To calculate it, I used Airphotoslive.com’s very striking images (MUCH larger than the thumbnail posted here)

Airphotoslive.com shot for CBS News

to make density estimates across different zones of the crowd; a variety of ground-level images from news photographers and attendees who posted their photos on Flickr; and Google Earth to measure the square footage of the different zones. Yes, I included the crowd areas under the trees; the full-size Airphotolive images were detailed enough to discern the edges of the crowd even there.

My estimate is that about 80,000 people were at the rally. Ryan Shuler, an Airphotoslive image analyst, used the same images and a different grid-density method to produce an estimate of 87,000. Considering the error margins around our separately-calculated estimates, they are statistically identical. CBS went with the 87,000 figure, which I certainly can accept.

Now the fun begins in the blogosphere. NBC News, the New York Times, and other large media outlets that didn’t attempt a scientific estimate uncritically accepted Beck’s claim of “300,000 to 500,000”. (At least Rep. Michelle Bachmann’s laughable claim of 1 million isn’t being treated seriously.)

The CBS News estimate immediately was vilified by conservative bloggers, and often rabidly-virulent comments from readers are being posted on news stories that mention the CBS estimate. I won’t post more links, but you can find plenty by Googling “beck rally attendance” and similar search terms.

The frothing underscores the problem with hyped predictions of crowd size. Organizers and supporters are forced to insist loudly that the actual crowd met or exceeded their expectations, for fear that the realistic estimate will be painted as a disappointment. The time-honored way to dismiss scientific estimates that don’t reflect the pre-event hype is to claim political bias on the part of those doing the estimate. I am amused to see that those who embraced my Obama inauguration estimate as soberly realistic are now attacking the Beck rally estimate, produced using exactly the same methods, as deliberately biased.

I expect that kind of behavior from partisans on both sides. I am disappointed, though, by the many responsible news organizations that failed to produce their own independent estimates and instead reported only ungrounded hype. Their readers and viewers deserve better journalism than that.

[DOIG afternote: I welcome reasoned comment and questions. Don’t bother sending ideological rants from any direction; I trash those. Also, it may take a while for your comment to be read and approved. I’m in Portugal five hours ahead of DC, also the flood of hits on the site has slowed it way down.]

[UPDATE: Those interested in this topic might also read this followup note.]

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