How many people attend the Ann Arbor Art Fair? I googled that question and found “over 500,000 visitors attend the fairs each year” (Wikipedia), “an estimated half-million visitors” ( AnnArbor.com), and “The Art Fairs attract over 500,000 visitors to the Ann Arbor area each year” ( visitannarbor.org). Sounds like an open-and-shut case.

But then I wondered: How do they know? How do they count?

One possibility: someone flew Rain Man up in a helicopter, where he made a quick count. Another option: birders used to estimate the numbers of migrating songbirds by counting how many cross the full moon in a given period of time. Then a simple process of geometry and arithmetic leads to an overall estimate. So someone sat at the window of Starbucks at Main and Liberty, counted the bodies going by, and applied some middle school math to come up with the figure. No?

My editor, who’s covered the fair for thirty years, tells me the number has been used for decades. It originated with fair publicist Dick Brunvand, who looked at the crowds and thought, “This is as busy as a football Saturday.” He took the capacity of Michigan Stadium, multiplied by four, and came up with an estimate of 400,000–a number that, soon enough, crept up to a round half-million.

When I checked with the directors of the four fairs, they confirmed that no one really knows how many people attend. Max Clayton, director of the Michigan Guild of Artists and Artisans, says that municipalities used to use police helicopters to estimate attendance, but that no longer occurs because of the cost involved. All four directors routinely photograph the streets at their fairs and then compare the crowd density to photos from previous years at the same time. Like counting migrating birds across the full moon? This method does not lead to a hard figure such as half a million, but it does lead to a feel for attendance trends.

Or does it? A couple of years ago, the Observer looked up figures for the number of people riding the AATA’s Art Fair shuttle buses over a fifteen-year period; the count had peaked in the mid-1990s, and had dropped since then by more than half. Yet the directors all say that attendance has remained steady, and according to Clayton may even be increasing. Mo Riley, director of the Original fair, says that it’s difficult to analyze attendance “because weather is a serious factor,” especially when using the snapshot method. And while attendance may appear to drop during the thunderstorms that are as much an Art Fair fixture as Mr. B, patrons all emerge from shelters, shops, and restaurants as soon as the “all clear”is given.

Mary Kerr, president of the Ann Arbor Convention and Visitors Bureau, tracks visitors to town and their economic impact by examining a number of factors on a monthly basis. Her office looks at such things as hotel occupancy and the number of tour buses coming to town (twenty to twenty-five every July), but she does not break out Art Fair week from the rest of the month, and when the month includes conventions of ironworkers and electricians it becomes impossible to isolate its impact. But, Kerr notes, “We do track the availability of rooms that week [of the Art Fair], and the last few years there have been rooms available–they were not 100 percent sold out.” Still, Kerr declines to say that points to a drop in attendance, and the directors are emphatic that attendance has remained strong.

So how do they judge attendance trends? “It’s experience,” Clayton says, to nods from the others. “How crowded does it feel? How long does it take to cross the street?” They supplement their experienced eyes with anecdotal reports from artists about the number of new people at their booths and increases in their mailing lists.

The creation of wider walking paths may make it more difficult to rely on experience and feeling. “We made a concerted effort,” Riley says, “to make traversing the Art Fair easier.” Maggie Ladd from the South U Fair concurs: “We reduced bottlenecks. It will look like less people.”

While Kerr reports that 2009 was a bad year economically for Ann Arbor and Michigan, with a gradual rebound in 2010 that she expects to continue through 2011, the Ann Arbor Art Fair saw no 2009 downturn. The directors attribute this to two factors: the loyalty of their “hard-core” fairgoers who would not miss it for the world, and “staycations” that meant folks traveled locally rather than to Petoskey or Italy.

Artist sales figures are another metric that could give a sense of Art Fair attendance, but since those figures are reported only on a voluntary basis with no way to confirm them, they are not much help. The state collects sales tax from the artists, but does not aggregate records for individual events. Kathy Krick, director of the State Street fair, says the high return rate of artists (and applications) indicates strong sales, which indicates the fairs are healthy. For artists, of course, sales are much more important than attendance data.

Another indication of health: it’s not unusual for artists who have been turned down for any one of the fairs to show up, spot an empty booth, and try to get “juried in” at the last minute.

Artists with whom I spoke describe Ann Arbor as a big moneymaker. Riley reports that sales of gift certificates, an innovation at the Original fair, are high–a good indication that whatever the size of the crowd, 2011 will be a good year for sales.