The police consistently underestimated the number of protestors by 20-30%, and the organizers consistently overstated them by at least 100%. Empirical research shows that the estimates are closer to the numbers claimed by the former rather than the latter.
June 9th claim 1.03 million: In an interview with the Columbia Journalism Review, Steve Doig, a professor specializing in data-based crowd-counting at Arizona State University questioned the number, stating that he would accept conservative estimates of a 250,000 protestors saying “If 7,000 people fit in 210 meters, there would need to be 142.9 street segments, or about 18.6 miles of streets packed at once to count a million protestors, which seems like too many for what was we saw in Hong Kong” source
Extrapolating these figures for the June 16 claim of two million marchers, you’d need a street 58km (36 miles) long. The main route of the march on that day was about 1.8 miles long. So for the protest to feature 2 million people, each protestor would have to repeat the route roughly 20 times over.
June 16th claim of 2 million: The HKPF gave a peak estimate of 338,000 attendees.
Bonnie Leung, the vice-convenor of CHRF told Reuters that they estimated their final count by manual counting: “We do a headcount by putting people up at the high points and count people one by one. So this is, I believe, the most laboring but scientific method of doing so,”.
Although the organizers declined to disclose how many people they deployed to count the crowd, counting at a rate of 10 people per second would take 55.5 man-hours of work while the protest lasted for 8 hours. Paul Yip Siu-fai, professor at the University of Hong Kong’s social sciences faculty, questioned the Civil Human Rights Front’s claimed method saying that a crowd of 2 million could not be counted manually.
HKUPOP, a politically neutral public opinion pollster provided an estimate of 500,000 to 800,000 protestors. Robert Chung, director of the program, said headcounts were getting hopelessly politicized and “less and less scientific”.
A picture widely shared by protest organizers and supporters such as Nathan Law of Demosisto echoing the 2 million figure was, in fact, a mirrored image source
July 1st claim of 550,000: The HKPF gave an official point-in-time count of 190,000. A team of social science and A.I researchers from Hong Kong University, Texas State University and C&R Wise AI (a technology company) teamed up to count the protestors. They used computer vision and A.I algorithms to count the number of protestors and stationed volunteers next to the cameras to help verify the count. They accounted for spillover into neighboring streets by setting up more cameras. They concluded that 265,000 people attended the march (half the number claimed by CHRF)
” The July 1 marches coincided with the ongoing anti-extradition bill protests. Organisers claim that around 550,000 people turned up to protest, a record-breaking turnout as the organisers claimed. However, police claimed 190,000 joined the protest rally. Researchers combining artificial intelligence and manual counting techniques concluded that a total of 265,000 people marched.Reuters counted the number of protestors at one location over 15 minute periods during the march and came to an estimate of 227,000 people in total. “