Estimates of numbers who marched on Tuesday vary widely
How many protesters took part in this year's July 1 march? The answer depends on whom you ask.
The annual pro-democracy march's organiser, the Civil Human Rights Front, put the turnout at 510,000, while the police said the number of marchers peaked at 98,600. They didn't offer an overall total.
Two academics from the University of Hong Kong estimated the total was between 122,000 and 172,000, while a method employed by the Post put the figure at 140,408. The wildest estimate, posted online, was 1.3 million.
The organisers said their figure was based on the average from three teams of volunteers counting at different points along the route, a method dismissed by University of Hong Kong statistician Professor Paul Yip Siu-fai as "almost impossible". Their base average was about 340,000, which the front multiplied by 1.5 on the grounds many protested on footpaths or outside the main route. That produced its final figure of about 510,000.
The 1.3 million estimate was based on a condensed version of a 90-minute YouTube video shot from a position above Victoria Park, where the march started.
Comments accompanying the film said the estimate was reached by assuming there were 20,000 people on each of the soccer pitches inside the park, or about six people per square metre - as crowded as an MTR compartment during peak hours.
The poster of the estimate claimed that over the 90 minutes taped, about 380,000 people had set off from the park. Multiplying that figure because the march lasted five hours produced the final total of 1.3 million.
The poster's assumption of crowd density does not seem to comply with the Jacobs' density rule, adopted by academics internationally, which assumes a loose crowd, with an arm's length between each person, has a density of about one person per square metre. A solid crowd has about two per square metre and a very dense one about four per square metre.
Dr Robert Chung Ting-yiu, the director of the University of Hong Kong's public opinion programme, employed the so-called count and follow-up method. His team selected an inspection point and counted the people who passed. A follow-up phone survey of city residents asked respondents whether or not they had passed the inspection point.
For this year's march, Chung's base figure was 111,670. While this year's phone poll result has yet to come in, last year's was used to produce a multiplier of 1.38 to 1.55, putting the final estimate at between 154,000 and 172,000.
Yip favours physically counting the crowd at two points, one near the end, which he said helped control for those who joined in the middle.
The police made their estimate based mainly on the size of Victoria Park and how crowded it appeared, they said.