Hi,
I have been trying to work out the sizes of some past protests, notably including the N30 protests in Seattle [November 30th, 1999].
If you have one big rally, the standard approach is to estimate the area of the rally, and its density, using the Jacobs Crowd Formula; if elevated or aerial photos exist, they can help.
If you have one big march, the standard approach is to wait beside the march, and count or sample the people passing by. Patrick Gillham got a count of about 35,000 people in the big labor march this way, but he might have missed some of the feeder or breakaway marches. Ron Judd estimated 36,000 to 44,000, extrapolating from rally size in the stadium.
In theory, you could also use the length and width of the march, and the pace, and the Jacobs Crowd formula, though you'd need lower densities for moving crowds. Has anyone tested appropriate densities, and appropriate march paces if you know the length in hours but not in blocks?
But what are good options if you have many small protests, or linked protests in adjacent blocks, or if you don't have some key data for bigger protests?
Is it possible to get better estimates out of individually-unreliable police and/or newspaper estimates?
At one point, I tried to use the Voices from the WTO collection as a sample of personal accounts, or use others I'd encountered in my research, and count how many people described being treated by protest medics (who subsequently reported treating 3,000 to 4,000 people), or described being arrested (police reported 603). But I don't think I have an unbiased sample.