The Hong Kong 7/1 March: Crowd Size Estimates (HKU: Yip Siu-fei team)

SOURCE #4:  HONG KONG UNIVERSITY STUDY (S.F. YIP) says 165,000

(Sing Tao)  Hong Kong University estimates only 200,000 marchers.  July 3, 2004.

[translation]  The 7/1 march is over and the organizers claimed a total of 530,000 marchers.  This number is relevant in forecasting the outcome of the September legco elections, but it has generated controversy.  A Hong Kong University Department of Statistics and Actuarial Science Senior Lecturer made a scientific calculation and estimated that 200,000 persons marched, a number that is about the same as the police estimate.  Civil Human Rights Front spokesperson Jackie Hung insisted that their estimate was accurate and emotionally said, "These academics ought to speak responsibly.  If they say that there were only 200,000, they are betraying those people who actually marched."

Hong Kong University Department of Statistics and Actuarial Science Senior Lecturer Yip Siu-fei was interviewed by our reporter and told us that his Department had sent people at two points of the march route and made precise counts.  He estimated that about 200,000 persons marched.

Yip Siu-fei emphasized that at those two points of observation, the personnel found that the maximum number of persons per minute was 600.  Since the march took 5.5 hours, it was estimated that a maximum of 200,000 could have been there.  This is about the same as the police estimate, but very much lower than the organizers' number.  Due to the sensitive nature of the crowd size estimate, Yip will write a detailed paper to explain the study design and the calculations.

Based with the challenges from the scholars, Civil Human Rights Front spokesperson Jackie Hung emphasized that they had held meeting with the police beforehand and was informed by the police that the roadway from Causeway Bay to Central can contain 170,000 people.  Since Victoria Park can contain 110,000 persons when full, there has to be almost 300,000 people and definitely more than 200,000.

Jackie Hung emotionally said, "These academics ought to speak responsibly.  If they say that there were only 200,000, they are betraying those people who actually marched."

Labor Alliance member Lee Chek-yan took part in the planning and said that 530,000 is an accurate number.  Over the three kilometers from Victoria Park to the Main Government Building, the six car lanes by one meter can contain about 60 people.  Therefore, three kilometers would contain about 170,000 persons.  These people took an average of 90 minutes to complete the walk.  There are three such groups of people in a 5-1/2 hour period.  From this, 530,000 is the proper estimate.

But Polytechnic University Applied Mathematics Department assistant professor Lee Leung-kwun belives that the Civil Human Rights Front did not account for statistical error in the calculation.  Over the three kilometer course, people walk at different pace.  Younger people walk faster, and families with children walk slower.  Furthermore, it was exceedingly hot out there.  When people take breaks and then rejoin, the numbers fluctuate.

Chinese University of Hong Kong Journalism and Communication School professor Chan To-man said that there was not need to worry about the numbers.  The most important thing is that the people are making a petition.  He pointed out that it is not an easy task to estimate the crowd size.  But the fact was that the citizens were not happy with the central government's rigid attitude, and this public march is a positive way of expressing their feelings. 

     七一大遊行」前天終告一段落，主辦單位民間人權陣報稱有五十三萬人上街，有關數字對評估九月選舉有一定參考作用，然而數字多寡昨日卻惹來爭議。港大統計及精算學系高級講師經科學統計後，推算出有二十萬人上街，與警方估計相若。民陣發言人孔令瑜堅持五十三萬人的推算準確，並語帶激動地說，「那些學者說話應該負責任，他們說有二十萬人，怎對得起參加遊行的巿民﹗」

　　香港大學統計及精算學系高級講師葉兆輝昨接受本報查詢時表示，該學系在前天七．一大遊行期間，在遊行沿途路兩個目標地點派員進行人數精算統計，確定約二十萬人上街。

　　葉兆輝強調，派員在兩個地點統計期間，發現平均每分鐘最高流量達六百人次，遊行歷時五個半小時內，經逐步推算，估計最多只有近二十萬名市民遊行，與警方估計相似，但與主辦的民陣推斷確有很大距離。由於遊行人數敏感，他稍後會將整個統計和推算方法詳細撰文，作出解釋。

　　面對學者質疑七．一大遊行五十三萬人上街，民陣發言人孔令瑜昨日強調，遊行前曾與警方開會，警方透露銅鑼灣至中環一段個半小時路段中，路面可容納達十七萬人次，維園擠滿則可容納十一萬人，至少在維園及街上已有近三十萬人，肯定不止二十萬人。

　　孔令瑜語帶激動地說，「那些學者說話應該負責任，他們說有二十萬人，怎對得起參加遊行的巿民﹗」她指過去以人手及遊行路面面積計算，是有一定可靠性。

　　有份策劃遊行的職工盟李卓人亦堅持，五十三萬人上街是一個正確數字，由維園至政府總部三公里路程中，平均每一米闊、六條行車長度的面積可容納近六十人，即三公里路程中可容十七萬人次，而每批人次花約個半小時完成，在五個半小時的遊行中分三批進行推斷，得出五十三萬人是正確數字。

　　不過，理工大學應用數學系助理教授李亮坤刖認為，民陣的推算方法沒有計算誤差，在整個三公里遊行路段中，市民各有不同速度，如年輕人較快速，一家大小帶同小朋友則會拖慢速度，加上天氣酷熱很多市民中途離隊稍作「」後，重新插回隊中，數字已有變化。

　　而中大新聞與傳播學院陳韜文教授則認為毋須太緊數字，最重要是巿民的訴求。他指計算遊行人數確實不易，但市民不滿中央強硬態度，上街遊行也是善意表達及正面訴求的方式。

On one hand, the HKU number is based upon the maximum flow.  The average flow is lower than the maximum, and the flow should be substantially less towards the end of the march.  So this is an over-statement.  On the other hand, the HKU number is an average flow number as opposed to a cumulative number.  If the crowd size is defined as the total number of people who marched on some portion of the route, then this is an understatement.

The preceding report was based upon preliminary results.  The full results were released a few days later in the form of a letter to the Sing Tao Daily.

(Sing Tao Daily)  Scholar says that fewer than 200,000 persons marched.  July 5, 2004.

[translation]  The Civil Human Rights Front announced that the number of 7/1 marchers was 530,000 and that has been challenged.  Hong Kong University Department of Statistics and Actuarial Science senior lecturer Yip Siu-fei wrote to this newspaper to claim that the total number of marchers is between 140,000 and 190,000 and no more than 200,000.  He pointed out that not only did the Civil Human Rights Front overclaimed the number of marchers in the last wave, but their assumption of a maximum density of 170,000 is also in error.

The scholar believes that the number of 7/1 marchers is only between 140,000 and 190,000.  In his letter to us, Yip Siu-Fei said that he and some graduate students and statistics majors formed a work group of 11 statisticians.  They set up two counting stations, on pedestrian overpasses in Causeway Bay and Taikoo Plaza (Admiralty) respectively.

He pointed out that the first group of marchers reached the Causeway Bay station at 245pm and the last group of marchers departed by 630pm.  On the average, about 8,000+ persons pass through that station every quarterhour.  After 600pm, the march route was reduced from 6 car lanes to 3 car lanes, so that the density could not continue to be assumed to be 170,000.  He estimated that the number of marchers who passed the Causeway Bay station to be 125,000.  Using the same method, the number of marchers who passed the Admiralty station to be 110,000.

In responding to questions from us, Yip Siu-fei pointed out that the counting project was challenged for not including those who join the march in the middle.  Therefore, they conducted interviews of marchers at Admiralty.  A sample of more than 600 marchers were interviewed, and 23% had joined in the march between the two counting stations.  Therefore, the total number of marchers was estimated as the 125,000 observed at the first station plus 23% of the 110,000 observed at the second station for a total of about 150,000.

They also considered that this method does not include three types of people: those who have left before reaching the first counting station, those who entered after the first counting station and left before the second counting station, and those who join the march after the second counting station.  Therefore, the team decided to add 10% more to adjust the total to 165,000.  The margin of error is 25,000.  In other words, the number is between 140,000 and 190,000, which is close to the police estimate.

Yip emphasized that the aerial photo analysis commissioned by a newspaper had significance implications.  The photos showed that at the peak of the march around 430pm, there were 72,000 persons on the road.  But the newspaper also double counted the number of people in the last wave and also did not consider the fact that the number of lanes was reduced.

He also pointed out that in addition to overstating the number of people in the third wave, the Civil Human Rights Front had another big problem by assuming the maximum density that can be carried on the road.  That is, 170,000 persons.  In order to achieve this density, there has to be 60 persons per row.  But based upon the observations, there were only between 20 to 30 persons per row.  The aerial photo analysis also showed that the density was much lower than the 170,000 used by the Civil Human Rights Front as the basis of their calculation.  This was therefore not a realistic assumption.

Tong Kam-Kuen is the general manager of Mathematics Specialist Educational Center, which provides mathematics courses to primary and secondary students, said that the Civil Human Rights Front overcounted the last wave.  In addition, the last wave took two hours to finish, which meant that they were going slower and slower.  Therefore to assume an average trip time of 90 minutes would overestimate the number of marchers.

He recommended that they should send monitors to accompany specific groups of people and then to count the appearance of these monitors at the start, midpoint and finish in order to estimate the number of marchers.

        民 間 人 權 陣  公 布 七 一 大 遊 行 人 數 為 五 十 三 萬 人 ， 再 受 質 疑 。 港 大 統 計 精 算 學 系 高 級 講 師 葉 兆 輝 在 本 報 來 論 ， 指 出 總 遊 行 人 數 介 乎 十 四 萬 至 十 九 萬 ， 不 超 過 廿 萬 人 ； 並 指 出 民 陣 的 方 法 除 了 重 複 計 算 了 最 後 一 程 人 數 外 ， 以 最 高 密 度 即 十 七 萬 人 作 計 算 基 礎 也 有 謬 誤 。

　 　 學 者 認 為 七 一 上 街 人 數 只 有 十 四 萬 至 十 九 萬 。 葉 兆 輝 在 本 報 來 論 指 出 ， 他 與 港 大 研 究 生 及 本 科 生 ， 組 成 十 一 人 的 遊 行 統 計 小 組 ， 分 別 於 銅 鑼 灣 及 金 鐘 太 古 廣 場 附 近 的 天 橋 上 ， 設 立 兩 個 點 算 站 。

　 　 他 指 出 ， 首 批 遊 行 人 士 於 二 時 四 十 五 分 到 達 銅 鑼 灣 點 算 站 ， 最 後 一 批 則 於 六 時 半 離 開 ， 平 均 每 十 五 分 鐘 約 八 千 多 人 經 過 該 站 ， 而 六 時 後 遊 行 路  由 六 條 行 車  變 成 三 條 ， 故 人 流 不 可 能 仍 然 是 十 七 萬 人 ， 估 計 遊 行 人 數 約 十 二 萬 五 千 。 以 同 樣 方 法 每 十 五 分 鐘 的 人 流 計 算 ， 約 十 一 萬 人 經 過 金 鐘 站 。

　 　 葉 兆 輝 回 覆 本 報 查 詢 時 指 ， 因 去 年 點 算 工 作 遭 質 疑 未 有 計 及 中 途 插 入 人 數 ， 故 今 年 特 別 於 金 鐘 站 ， 在 不 同 時 段 抽 樣 訪 問 六 百 多 人 ， 發 現 兩 成 三 受 訪 者 在 兩 個 點 算 站 中 途 加 入 ， 故 總 體 人 數 是 第 一 個 點 算 站 的 十 二 萬 五 千 ， 再 加 第 二 個 站 人 數 十 一 萬 的 兩 成 三 ， 即 十 五 萬 左 右 。

　 　 考 慮 到 這 計 法 未 有 包 括 三 類 人 士 ﹕ 即 未 到 第 一 個 站 已 離 開 、 在 兩 個 站 中 途 加 入 及 離 開 、 在 第 二 站 之 後 才 加 入 的 人 ， 小 組 決 定 多 加 百 分 之 十 ， 把 總 人 數 調 整 為 十 六 萬 五 千 人 ， 整 體 估 計 誤 差 為 二 萬 五 千 人 。 換 言 之 ， 介 乎 十 四 萬 至 十 九 萬 ， 與 警 方 的 數 字 相 近 。

　 　 他 強 調 ， 由 報 章 委 託 進 行 的  星 圖 片 分 析 具 重 要 參 考 價 值 ， 圖 片 顯 示 四 時 半 的 高 峰 期 路 面 有 七 萬 二 千 人 ， 只 是 該 報 重 複 計 算 了 最 後 一 程 人 數 及 未 有 計 及 路 面 收 窄 。

　 　 他 指 出 ， 民 陣 除 了 重 複 計 算 最 後 一 程 人 數 ， 最 大 問 題 是 它 採 用 路 面 可 容 納 的 最 高 人 潮 密 度 、 即 十 七 萬 人 作 計 算 基 礎 ， 要 達 這 密 度 ， 平 均 要 六 十 人 一 排 ， 但 按 當 日 點 算 ， 平 均 只 有 二 十 至 三 十 人 一 排 ， 加 上  星 圖 片 顯 示 的 人 潮 密 度 亦 遠 低 於 故 民 陣 堅 持 採 用 十 七 萬 成 計 算 基 礎 ， 是 有 點 未 能 反 映 實 際 情 況 。

　 　 為 中 小 學 生 提 供 數 學 專 科 課 程 的 數 學 專 門 店 教 育 中 心 業 務 總 監 湯 錦 權 亦 指 ， 民 陣 的 方 法 重 複 計 算 了 最 後 一 程 ， 而 且 最 後 一 批 人 士 花 了 兩 小 時 才 完 成 ， 可 見 隊 伍 愈 行 愈 慢 ， 以 每 程 一 點 五 小 時 計 算 ， 已 高 估 了 人 數 。

　 　 他 建 議 每 隔 某 特 定 人 數 便 加 入 一 糾 察 員 跟 隨 大 隊 ， 再 派 人 於 起 點 、 中 途 及 終 點 ， 點 算 糾 察 出 現 的 次 數 ， 再 推 算 出 人 數 。

I was unable to locate a copy of Yip Siu-Fei's letter on the Sing Tao website.  So I am including a translation from the printed edition.

[translation]  The issue of whether the number of 7/1 marchers is 530,000 or 200,000+ is a point of debate for this year's march.  Senior lecturer Yip Siu-fei from Hong Kong University Department of Statistics and Actuarial Science wrote a letter to Sing Tao Daily to explain in detail the methodology used by him and his team of graduate students to deduce that the number of marchers was fewer than 200,000.

The task of estimating the number of people in a march is challenging because we have to estimate the size of a mobile population in which people may join or leave the march at various points.  The author formed a team consisting of graduate students and student majors at Hong Kong University.  On the day of July 1st, we conducted a detailed research study on site.

Our team set up two counting stations, one at the Causeway Bay Electronics Center (near the starting point at Victoria Park) and at the pedestrian overpass near Taikoo Plaza at Admiralty near the Central Government Office.  At each counting station, three workers independently counted the number of marchers for the entire march period.

Using the Causeway Bay station as an example, the first group of marchers reached the station around 245pm, and the last group of marchers passed that station around 630pm.  On the average, there were 8,750 persons passing the station every 15 minutes.  The maximum number was around 10,000, which was recorded between 500pm and 515pm.  Because the march route was reduced from six car lanes to three car lanes at the first and second counting stations at 6pm and 7pm respectively, the flow of marchers was significantly reduced after 6pm.

After adding up across the various periods of time, we estimated that a total of 125,000 persons passed through the Causeway Bay counting station.  Even if we applied the highest density, the maximum number of marchers was only about 140,000.  Using the same method, about 110,000 people passed by the Admiralty counting station.   The counts obtained at the two stations would include people who joined or left the march.

To estimate the number of people who joined or left the march in the middle, the team also sampled marchers at the second counting station.  At various times, we asked the marchers: "During this march, did you go past the Sogo Department Store?"  We used this to adjust estimate the number of people who joined the march midway.  For example, if we found that 100% of the people said yes, then everyone who passed the second station also passed the first station, so the number of marchers at the first station could be used as the march total.  If 0% said yes, this means everyone who passed the first station left the march and everyone who passed the second station joined midway.  The number of marchers in this case would be the sum of the two counts.

Of the people who passed by the second counting station, we sampled more than 600 persons.  77% of them said that they passed by the Sogo Department Store, which meant that 23% of the marchers had joined in the middle.  The total number of marchers is therefore 125,000 at the first counting station plus 23% of the 110,000 at the second counting station.  This is around 150,000.

Of course, this calculation three types of people: (1) those who left Victoria Park but never made it to the first counting station.  This should be a very small number because it is only 15 minutes from the start; (2) those who joined after the first counting station but left before the second counting station; (3) those who joined the march after the second counting station.

Based upon the actual observations of the team, the march was well-disciplined and there should not be very many of these three types of people.  The team decided to add 10% to the total so that the number of marchers is estimated to be 165,000.  The margin of error is 25,000, which would make it close to the police estimate of 200,000.

I will now make some comparison with estimates made by other organizations.  The aerial photo analysis offered some relevant information.  At the peak time of 430pm, there were 72,000 persons on the entire route.  If we adjust for their error of overcounting the last wave as well as the closing of the roadway at the end, the estimated number would be around 170,000.

As for the 530,000 estimate from the Civil Human Rights Front, if we correct for the over-counting of the last wave and then used the 72,000 density from the aerial photos as the basis, plus the 20,000 hypothetical added marchers who joined in the middle, the number would be 176,000, which is close to our estimate.  Actually, the 170,000 figured used by the Civil Human Rights Front was based upon the maximum capacity estimated by the police.  But based upon the actual observation that day, there was rarely any situation in which the density was like 60 persons per row.  In order to accurately estimate the density flow of the crowd, the team has captured the march on film and have repeatedly examined for reference.  Those interested may also use this as reference.

Our team conducted this project with limited resources on an independent basis in the quest for knowledge.  We used two counting stations supplemented by intercept surveys, and this is an innovative attempt.  Our team members stayed with the jobs until the entire march was over, and this reflects our serious attitude in addressing this sensitive question.  Finally, the marchers should be proud that they used peaceful and rational methods to express their requests under the hot sun.

This study has the best methodology so far, ahead of sources 1 through 4.  Of the three possible leakages that they identified, the first and third must be miniscule.  How many people would start out from Victoria Park and drop out several minutes later?  How many people would join the march right before reaching the Central Government Office?  There is about an hour's walking time time between the Sogo Department Store and Taikoo Plaza, but it is probably too generous to attribute a 10% lift for those who joined after Sogo but left before Takoo Plaza to the total.

On July 9, 2004, Sing Tao Daily published a delayed interview with Yip Siu-Fai.  The reason for the delay is given at the end of the article.  This article is heart-rendingly sad in terms of its implications for freedom of speech and the pursuit of truth under 'democracy.'

[translation]  Speaking about the recent criticism, Yip Siu-fei looked as if he did not know where to begin.  "Actually, you could classify me as a pan-democrat ... but maybe I would not say that because this is going to draw criticisms such as 'How can you possibly be a pan-democrat?'  Anyway, I support the 7/1 march and I was a member of the march."

At a time when emotions are surging, Yip Siu-fei published a smaller estimate of crowd site.  He foresaw that he would be regarded as being on the wrong side: "My thirteen-year-old son said, 'Daddy, aren't you afraid of being slammed(炳)?'  But I feel that I am not trying to be contrarian and I am only telling the facts according to the data."  He believes that those who support democracy also believe in justice and honor the facts.

Moreover, he thinks that an "exaggerated number" is not necessarily good for those who marched for democracy.  "It creates a mistaken hope to let people feel that it would be a big letdown if there were fewer than 500,000 the next time.  If we accept 530,000 this time, then are we going to have to get 1 million next year?" said Yip Siu-Fei.

On the day of the march, he and his students set up two counting stations at Victoria Park and Admiralty, working from after 2pm to after 7pm.  "The numbers were 125,000 at Causeway Bay and more than 110,000 at Admiralty.  Even if all the 125,000 at Causeway Bay left before the finish and all the 110,000 at Admiralty joined in the middle, the sum if still less than 530,000.  His method is to obtain counts of the flow every 15 minutes, and then interviewed a sample of marchers to estimate the number that joined in the middle.  The estimated number of marchers was 165,000 with a margin of error of 25,000.

At last year's 7/1 march, his estimate on the number of marchers was 250,000, which was criticized by academics.  "Last year, I did not account for the number of marchers who joined in the middle.  Therefore I included this category in my new calculations and the number is now more complete."  Yip Siu-fei's voice showed the happiness of a child and he was obviously delighted with having found a more accurate method.  He said that he will publish a paper on this method.

"I also feel that I have to say something about the police.  Why do people feel that the police underestimated the number of marchers?"  Yip Siu-fei said that the police estimate was closer to scientific data.  "Someone said to add the police and civil numbers together and divide by two to get the right answer.  This is unscientific."

"7/1 is an important event and many people pay attention, in Hong Kong and internationally.  It has a huge impact.  Actually, any march over 100,000 people is already a significant event.  Just think, even if the anti-Article 23 march had 6,000 or 10,000 people, it would not have been ignorable.  Once the number gets past a certain point, it cannot be ignored."

He remembered that at the time of the June 4 incident in 1989, he was teaching at Melbourne University.  He heard about the suppression of the students at Tienanmen Square and that the local Chinese community was going to hold a demonstration.  On that day, he "cut class" and left his students to march.  "The local students were very understanding, because they felt that this was a very important matter."

A supporter of marching to express demands, he frankly admits that there were pressures in publishing the estimate of the marchers this time.  "Some students participated in this research.  Prior to publication, we discussed this.  Our final decision was to proceed to publish, because we believe that this number is closer to the facts and the citizens should know that democracy means respecting the facts" said Yip Siu-Fei.

Yip Siu-fei grew up in an ordinary middle-class family.  He went to attend university in Australia.  In 1991, he began to teach at Hong Kong University.  Every time that some new statistics appear, his name would appear in the newspapers.  He uses his knowledge of statistics to analyze the social phenomena contained in population growth rates, suicide rates, birth rates, population aging and other statistics.  As for estimating crowd sizes in marches, 7/1 last year was his first time and 7/1 this year was his second time.  Two months ago, he discussed the method of calculation with academics in Taiwan.

"This number is important and it is in my area of specialty.  That is why I did it."  Yip Siu-fei said that he disagreed with the 530,000 number, but he resolutely believes that the democrats did not engage in 'exaggeration.'  The estimation of crowd size needs specialized knowledge and experience.

This interview was conducted on Monday.  That afternoon, he learned that the Civil Human Rights Front was going to hold a press conference about the number of marchers.  At that time, he hesitated and asked our reporter to delay the publication of this interview.  He said that he does not doubt the scientific basis of his data, but he was concerned that the timing was too sensitive because it creates the impression of intentional opposition: "We are only academics.  We don't want to engage in political fights.  I only want to find out what the data say."

Yip Siu-fei's remarks above included this: "If we accept 530,000 this time, then are we going to have to get 1 million next year?"  In the South Morning China Post on July 11th, the following story appeared:

Two pro-democracy groups yesterday warned the government to brace for even bigger marches next year unless it heeds public demands for universal suffrage in 2007-08.

The Frontier and the Association for Democracy and People's Livelihood (ADPL) sounded the warning after meeting Chief Executive Tung Chee-hwa.

If this year's number was in fact inflated, then this would be a serious disservice.  Given the storm about the estimates this year, I must take it that there will be a properly designed, executed and audited study next year and the best methodology so far is the HKU one.  If the true number was about 200,000 this year, then it would be very difficult to reach 500,000 next year in the absence of new external developments.  Time is now on the side of the central government, since they will presumably be sending more economic gifts to Hong Kong.  If next year's number is 300,000, then this would be taken to be a big drop in popular sentiments from the 530,000 claimed for this year.  If this year's number had been accepted as 200,000, then a 300,000 would have been a big increase.  This will be the historical baggage that the Civil Human Rights Front bequeathed to the cause of democracy.

On July 11th, another member of the HKU team, Chan Kin-sun, who is a doctoral graduate in the Hong Kong University Social Work and Social Administration Department, wrote in Sing Tao Daily:

[translation]  The author was fortunate to participate in the research led by professor Yip Siu-fei to estimate the number of marchers, and is a co-author of the article in Sing Tao Daily with professor Yip Siu-fei.

Whether the number of marchers is 500,000 or 200,000 does not have a lot of impact on the impact of this march.  The more important thing was that the voice of the marchers must be reflected.  But the author did not expect that a seemingly minor issue of the estimation of the number of marchers would cause certain politicians to misunderstand people in the academic field.  This is really unfortunate.

There is no method that is 100% perfect, and therefore the so-called 'actual numbers' can only be determined via certain methods of estimation that contain some errors.  We believe that various researchers or organizations would like to use the best method of estimation (or, at least, the method with the smallest error) for the number of marchers in order to do justice for those who marched in the hot weather and to all the citizens of Hong Kong.

Whether it is the aerial photo analysis, the formula used by the Civil Human Rights Front or the field counts, or even the opinion polls, all these methods have certain credibility and logic in order to be accepted.  At the same time, these methods surely contain certain errors and assumptions.  The problem today is that, apart from the CHRF estimate, all the other organizations obtained numbers that are similar --- from 165,000 to 260,000.  These are independent organizations, so it is hard to assert that they are directed by the central government or SAR government.  It is hard to imagine that these organizations would collude to negate the CHRF number and to deflate the number of marchers.

As well, these organizations have all prepared data files, such as the aerial photos and video films of the entire march, which would permit others to verify the accuracy of the numbers; by comparison (to the regret of this author), the CHRF has not offered any new evidence to support their hypothesis, such as each trip having 170,000 persons (which may be the maximum capacity estimated by the police) and each trip taking 90 minutes (which may be the average time to cover the distance on an ordinary day), and how to verify these hypothetical numbers.  Purely on the basis of 'instinct' and a group of monitors who had to maintain order and count at the same time seems amazingly crude.  The most incomprehensible thing is that the CHRF entirely denied the reliability and utility of the aerial photo data (or could it be because the estimated number was only 72,000?).

On the number of trips, it was rounded to 3.  But 2.66 compared to 3 is already a 10% discount.  This is acknowledged by professor Law Chi-kwong.  At the end of the march (that, is the final half hour), the route has been reduced from 6 lanes to 3 lanes so that is another further 5% reduction.

The 90 minute length of the trip is also suspect  It was extremely hot that day, so it is highly possible that the pace would be slower.  If there were really 170,000 people as asserted by the CHRF, there should be about 60 persons per row.  It is not hard to imagine that there would be traffic congestion, leading to a vastly reduced pace.  If as suggested by some readers, one trip could take 120 minutes, then there were only two trips.  Based on this, the whole number could be discounted by another 25%.

If all of the above conditions were true, the number of marchers would be exactly 164,000 (=2 x 72,000 + 20,000) and the CHRF estimate would be about the same as the estimates of the other organizations.

Of course, people can criticize this method for understating the actual number of marchers.  But every assumption in there is not invented out of the air.  In practice, every assumption used by the CHRF was based upon the maximum value, such as the maximum capacity and normal pace.  The assumed values used by the CHRF exceeds those used by other organizations, and so it is not hard to understand why their final value is much higher.

Since whether the number is 200,000 or 500,000 does not change the meaning of the 7/1 march, then why is the CHRF so rigid on this dispute between 200,000 and 500,000?  Since all the organizations used scientific methods and actual data as their basis and they all came out around 200,000, why does the CHRF insist on its own number?

If the CHRF really believes that there were 500,000 persons at the march, then we ask the CHRF to give the citizens a lesson on how there were 170,000 persons on the route (and therefore not the 72,000 seen in the aerial photos), 20,000 joined the march in the middle and the march averaged 90 minutes.  We ask them to instruct us on methods and data that would allow us to verify those numbers.

If there are no related data, then how can we assure that the counts from the CHRF monitors could be more accurate that the other organizations that estimated the number of marchers?  Please do not just say that the other methods contain flaws and then gloss the assumptions and calculations for the "500,000" number.  This is going to damage the honesty and trustworthiness of the pan-democratic camp, and therefore hindering the quest for democracy in Hong Kong.

Justice is not just the goal of the democrats, for it is the goal of all Hong Kong citizens.  Justice covers both fairness and transparency.  But in explaining the process of calculating the number of marchers, the CHRF did not explain how the various factors came about so that is was impossible to assess the reliability of these factors.

I remember the CHRF spokesperson's famous strong sentence: "How can they (the academics) face the citizens who marched when they say only 200,000?"  Now they are saying, "Justice is in the heart of the people" or "Let the citizens decide for themselves."  How can this be a just expression?

Finally, the author points out that our group did not receive any support from any political organizations or the government.  We only wanted to put theory into practice to find a more realistic number.  The author is not anti-democratic, and wishes to see direct elections take place in Hong Kong as quickly as possible.

But the author is against using extreme inflammatory methods to fight for democracy, especially against the use of "seemingly exaggerated" and "lacking data support" estimates of the number of marchers to fight for democracy.

The author wrote this letter because the author believes (as does most of the pan-democratic camp should agree as well) that democracy obtained by fair methods is the democracy that the citizens of Hong Kong desire.  We do not want a democratic society that wants 'quantity' more than 'quality.'