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'''Six degrees of separation''' is the idea that all people on average are six, or fewer, social connections away from each other. Also known as the 6 Handshakes rule. As a result, a chain of "[[Friend of a friend|a friend of a friend]]" statements can be made to connect any two people in a maximum of six steps. It was originally set out by [[Frigyes Karinthy]] in 1929 and popularized in an eponymous [[Six Degrees of Separation (play)|1990 play]] written by [[John Guare]]. It is sometimes generalized to the average [[Path length|social distance]] being [[logarithm]]ic in the size of the population.

'''Six degrees of separation''' is the idea that all people on average are six, or fewer, social connections away from each other. Also known as the 6 Handshakes rule. As a result, a chain of "[[Friend of a friend|a friend of a friend]]" statements can be made to connect any two people in a maximum of six steps. It was originally set out by [[Frigyes Karinthy]] in 1929 and popularized in an eponymous [[Six Degrees of Separation (play)|1990 play]] written by [[John Guare]]. It is sometimes generalized to the average [[Path length|social distance]] being [[logarithm]]ic in the size of the population.

'''六度分隔理论（Six degrees of separation）'''是指所有的人平均有六个，或更少的社会关系，彼此之间的关系。也被称为6次握手规则。因此，一个 "朋友的朋友 "的声明链可以在最多六个步骤中把任何两个人联系起来。它最初是由Frigyes Karinthy在1929年提出的，并在John Guare于1990年创作的同名戏剧中得到推广。它有时被概括为平均社会距离是人口规模的对数。

'''六度分隔理论（Six degrees of separation）的观点'''是指平均只需要六个人或者更少，就可以和世界上任意的人建立联系，也被称为'''6次握手规则（the 6 Handshakes rule）'''。基于“朋友的朋友”的这个关系，两两联系可以得到最多不超过六个步骤就可以把世界中任何两个人联系起来。最初由Frigyes Karinthy在1929年提出，并在John Guare于1990年创作的同名戏剧中得到推广。它有时被概括为平均社会距离是人口规模的对数。

 

 

== 初期概念 ==

== 初期概念 ==

=== 缩小的世界 ===

=== 缩小的世界 ===

Theories on optimal design of cities, city traffic flows, neighborhoods, and demographics were in vogue after [[World War I]]. These{{Citation needed|date=January 2010}}<!--What does statism have to do with this? Has some paranoic Libertarian been at work even here? ... Formally, I'm requesting a citation for the claim that the Karinthy story is connected to "statism" in city design.--> conjectures were expanded in 1929 by [[Hungary|Hungarian]] author [[Frigyes Karinthy]], who published a volume of short stories titled ''Everything is Different.'' One of these pieces was titled "Chains," or "Chain-Links." The story investigated{{snd}} in abstract, conceptual, and fictional terms{{snd}} many of the problems that would captivate future generations of mathematicians, sociologists, and physicists within the field of network theory.<ref name=newman>Newman, Mark, Albert-László Barabási, and Duncan J. Watts. 2006. ''The Structure and Dynamics of Networks.'' Princeton, NJ: Princeton University Press.</ref><ref name=bara/> Due to technological advances in communications and travel, friendship networks could grow larger and span greater distances. In particular, Karinthy believed that the modern world was 'shrinking' due to this ever-increasing connectedness of human beings. He posited that despite great physical distances between the globe's individuals, the growing density of human networks made the actual social distance far smaller.<ref name=":0">[https://djjr-courses.wdfiles.com/local--files/soc180%3Akarinthy-chain-links/Karinthy-Chain-Links_1929.pdf Karinthy, Frigyes. (1929) "Chain Links."]</ref>

Theories on optimal design of cities, city traffic flows, neighborhoods, and demographics were in vogue after [[World War I]]. These{{Citation needed|date=January 2010}}<!--What does statism have to do with this? Has some paranoic Libertarian been at work even here? ... Formally, I'm requesting a citation for the claim that the Karinthy story is connected to "statism" in city design.--> conjectures were expanded in 1929 by [[Hungary|Hungarian]] author [[Frigyes Karinthy]], who published a volume of short stories titled ''Everything is Different.'' One of these pieces was titled "Chains," or "Chain-Links." The story investigated{{snd}} in abstract, conceptual, and fictional terms{{snd}} many of the problems that would captivate future generations of mathematicians, sociologists, and physicists within the field of network theory.<ref name=newman>Newman, Mark, Albert-László Barabási, and Duncan J. Watts. 2006. ''The Structure and Dynamics of Networks.'' Princeton, NJ: Princeton University Press.</ref><ref name=bara/> Due to technological advances in communications and travel, friendship networks could grow larger and span greater distances. In particular, Karinthy believed that the modern world was 'shrinking' due to this ever-increasing connectedness of human beings. He posited that despite great physical distances between the globe's individuals, the growing density of human networks made the actual social distance far smaller.<ref name=":0">[https://djjr-courses.wdfiles.com/local--files/soc180%3Akarinthy-chain-links/Karinthy-Chain-Links_1929.pdf Karinthy, Frigyes. (1929) "Chain Links."]</ref>

关于城市的优化设计、城市交通流、邻里关系和人口统计学的理论在第一次世界大战后大行其道。这些猜想在1929年被匈牙利作家Frigyes Karinthy扩展，他出版了一卷短篇小说，题为《万物皆不同》。其中一篇题为 "链子"，或 "链子"。这个故事以抽象、概念和虚构的方式研究了许多问题，这些问题将吸引未来几代网络理论领域的数学家、社会学家和物理学家。<ref name="newman" /><ref name="bara" />由于通信和旅行方面的技术进步，友谊网络可以变得更大，跨越更远的距离。特别是，卡林西认为，由于人类的这种不断增加的联系，现代世界正在 "缩小"。他认为，尽管全球个人之间有很大的物理距离，但人类网络的密度不断增加，使得实际的社会距离大大缩小。<ref name=":0" />

关于城市的优化设计、城市交通流、邻里关系和人口统计学的理论在第一次世界大战后颇为流行。这些猜想在1929年被匈牙利作家Frigyes Karinthy扩展，他出版了一卷题为《万物皆不同》短篇小说。其中一篇题为 "链"，或 "链接"，这个故事以抽象、概念和虚构的方式研究了许多问题，这些问题吸引了众多未来几代网络理论领域的数学家、社会学家和物理学家。<ref name="newman" /><ref name="bara" />由于通信和旅行方面的技术进步，友谊网络可以变得更大，跨越更远的距离。特别是，卡林西认为，人类的这种不断增加的联系，导致现代世界正在 "缩小"。他认为，尽管全球个人之间有很大的物理距离，但人类网络的密度不断增加，使得实际的社会距离大大缩小。<ref name=":0" />

As a result of this hypothesis, Karinthy's characters believed that any two individuals could be connected through at most five acquaintances. In his story, the characters create a game out of this notion. He wrote:

As a result of this hypothesis, Karinthy's characters believed that any two individuals could be connected through at most five acquaintances. In his story, the characters create a game out of this notion. He wrote:

A related theory deals with the quality of connections, rather than their existence. The theory of [[three degrees of influence]] was created by Nicholas A. Christakis and James H. Fowler.{{Citation needed|date = July 2016}}

A related theory deals with the quality of connections, rather than their existence. The theory of [[three degrees of influence]] was created by Nicholas A. Christakis and James H. Fowler.{{Citation needed|date = July 2016}}

A related theory deals with the quality of connections, rather than their existence. The theory of three degrees of influence was created by Nicholas A. Christakis and James H. Fowler.

与此相关的理论有三度影响理论（The theory of [[three degrees of influence]] ）是由Nicholas A. Christakis 和 James H. Fowler提出的，这个类似的理论提出链接的质量远远大于其存在（质量高的一个关系远远大于众多低质量的关系）。

Michael Gurevich conducted seminal work in his empirical study of the structure of social networks in his 1961 [[Massachusetts Institute of Technology]] PhD dissertation under [[Ithiel de Sola Pool]].<ref name=":1">Gurevich, M (1961) The Social Structure of Acquaintanceship Networks, Cambridge, MA: MIT Press</ref> Mathematician [[Manfred Kochen]], an Austrian who had been involved in urban design, extrapolated these empirical results in a mathematical manuscript, ''[[Contacts and Influences]]'',<ref name=":2">de Sola Pool, Ithiel, Kochen, Manfred (1978–1979)."Contacts and influence." ''Social Networks'' 1(1): 42</ref> concluding that in a U.S.-sized population without social structure, "it is practically certain that any two individuals can contact one another by means of at most two intermediaries. In a [socially] structured population it is less likely but still seems probable. And perhaps for the whole world's population, probably only one more bridging individual should be needed." They subsequently constructed [[Monte Carlo method|Monte Carlo]] simulations based on Gurevich's data, which recognized that both weak and strong acquaintance links are needed to model social structure. The simulations, carried out on the relatively limited computers of 1973, were nonetheless able to predict that a more realistic three degrees of separation existed across the U.S. population, foreshadowing the findings of American psychologist [[Stanley Milgram]].{{Citation needed|date = July 2016}}

Michael Gurevich conducted seminal work in his empirical study of the structure of social networks in his 1961 [[Massachusetts Institute of Technology]] PhD dissertation under [[Ithiel de Sola Pool]].<ref name=":1">Gurevich, M (1961) The Social Structure of Acquaintanceship Networks, Cambridge, MA: MIT Press</ref> Mathematician [[Manfred Kochen]], an Austrian who had been involved in urban design, extrapolated these empirical results in a mathematical manuscript, ''[[Contacts and Influences]]'',<ref name=":2">de Sola Pool, Ithiel, Kochen, Manfred (1978–1979)."Contacts and influence." ''Social Networks'' 1(1): 42</ref> concluding that in a U.S.-sized population without social structure, "it is practically certain that any two individuals can contact one another by means of at most two intermediaries. In a [socially] structured population it is less likely but still seems probable. And perhaps for the whole world's population, probably only one more bridging individual should be needed." They subsequently constructed [[Monte Carlo method|Monte Carlo]] simulations based on Gurevich's data, which recognized that both weak and strong acquaintance links are needed to model social structure. The simulations, carried out on the relatively limited computers of 1973, were nonetheless able to predict that a more realistic three degrees of separation existed across the U.S. population, foreshadowing the findings of American psychologist [[Stanley Milgram]].{{Citation needed|date = July 2016}}

迈克尔-古雷维奇在1961年麻省理工学院伊瑟尔-德-索拉-波尔的博士论文中对社会网络结构进行了开创性的研究。<ref name=":1" />数学家曼弗雷德-科亨，一位从事城市设计的奥地利人，在一份数学手稿《接触和影响》中推断了这些经验结果，<ref name=":2" />结论是在一个没有社会结构的美国规模的人口中，"实际上可以肯定，任何两个人可以通过最多两个中间人的方式互相接触。在一个[社会]结构的人口中，这种可能性较小，但似乎仍有可能。而对于整个世界的人口来说，可能只需要多一个搭桥的个体"。他们随后根据古列维奇的数据构建了蒙特卡洛模拟，该模拟认识到弱的和强的熟人联系都需要建立社会结构模型。在1973年相对有限的计算机上进行的模拟，仍然能够预测美国人口中存在更现实的三度分隔，这预示着美国心理学家斯坦利-米尔格伦的发现。

迈克尔-古雷维奇Michael Gurevich师从[[Ithiel de Sola Pool]]<ref name=":1" />，在1961年麻省理工学院的博士论文中对社会网络结构进行了开创性的研究。<ref name=":1" />数学家[[Manfred Kochen]] 是以为从事城市设计的奥地利人，在一份数学手稿《接触和影响》''[[Contacts and Influences]]''<ref name=":2" /> 中也提出了类似的推断：在一个没有社会结构的，有美国人口规模的群体中，"实际上可以肯定，任何两个人可以通过最多两个中间人的方式互相接触。而在一个有'''社会结构的'''人口中，这种可能性较小，但似乎仍有可能。对于整个世界的人口来说，可能只需要多一个搭桥的个体"。他们随后根据古列维奇的数据构建了蒙特卡洛模拟，该模拟认识到弱的和强的熟人联系都需要建立社会结构模型。在1973年相对有限的计算机上进行的模拟，仍然能够预测美国人口中存在更现实的三度分隔，这预示着美国心理学家斯[[Stanley Milgram]]的发现。

Milgram continued Gurevich's experiments in acquaintanceship networks at [[Harvard University]] in Cambridge, Massachusetts, U.S. Kochen and de Sola Pool's manuscript, ''Contacts and Influences'',<ref name=":3">de Sola Pool, Ithiel, Kochen, Manfred (1978–1979)."Contacts and Influence." ''Social Networks'' 1(1): 5–51</ref> was conceived while both were working at the [[University of Paris]] in the early 1950s, during a time when Milgram visited and collaborated in their research. Their unpublished manuscript circulated among academics for over 20 years before publication in 1978. It formally articulated the mechanics of social networks, and explored the mathematical consequences of these (including the degree of connectedness). The manuscript left many significant questions about networks unresolved, and one of these was the number of degrees of separation in actual social networks. Milgram took up the challenge on his return from [[Paris]], leading to the experiments reported in ''The Small World Problem'' <ref name="Stanley Milgram 1968">{{cite journal | last1 = Milgram | first1 = Stanley | year = 1967 | title = The Small World Problem | url = | journal = Psychology Today | volume = 2 | issue = | pages = 60–67 }}</ref> in popular science journal ''[[Psychology Today]]'', with a more rigorous version of the paper appearing in [[Social Psychology Quarterly|Sociometry]] two years later.<ref name=":4">Travers, Jeffrey, and Stanley Milgram, [http://www.cis.upenn.edu/~mkearns/teaching/NetworkedLife/travers_milgram.pdf "An Experimental Study of the Small World Problem"], Sociometry 32(4, Dec. 1969):425–443</ref> The ''Psychology Today'' article generated enormous publicity for the experiments, which are well known today, long after much of the formative work has been forgotten.

Milgram continued Gurevich's experiments in acquaintanceship networks at [[Harvard University]] in Cambridge, Massachusetts, U.S. Kochen and de Sola Pool's manuscript, ''Contacts and Influences'',<ref name=":3">de Sola Pool, Ithiel, Kochen, Manfred (1978–1979)."Contacts and Influence." ''Social Networks'' 1(1): 5–51</ref> was conceived while both were working at the [[University of Paris]] in the early 1950s, during a time when Milgram visited and collaborated in their research. Their unpublished manuscript circulated among academics for over 20 years before publication in 1978. It formally articulated the mechanics of social networks, and explored the mathematical consequences of these (including the degree of connectedness). The manuscript left many significant questions about networks unresolved, and one of these was the number of degrees of separation in actual social networks. Milgram took up the challenge on his return from [[Paris]], leading to the experiments reported in ''The Small World Problem'' <ref name="Stanley Milgram 1968">{{cite journal | last1 = Milgram | first1 = Stanley | year = 1967 | title = The Small World Problem | url = | journal = Psychology Today | volume = 2 | issue = | pages = 60–67 }}</ref> in popular science journal ''[[Psychology Today]]'', with a more rigorous version of the paper appearing in [[Social Psychology Quarterly|Sociometry]] two years later.<ref name=":4">Travers, Jeffrey, and Stanley Milgram, [http://www.cis.upenn.edu/~mkearns/teaching/NetworkedLife/travers_milgram.pdf "An Experimental Study of the Small World Problem"], Sociometry 32(4, Dec. 1969):425–443</ref> The ''Psychology Today'' article generated enormous publicity for the experiments, which are well known today, long after much of the formative work has been forgotten.

米尔格拉姆在美国马萨诸塞州剑桥市的哈佛大学继续进行古雷维奇的熟人网络实验。科琴和德索拉-波尔的手稿《接触与影响》<ref name=":3" />是两人在20世纪50年代初在巴黎大学工作时构思的，当时米尔格拉姆访问并合作进行研究。他们未发表的手稿在学术界流传了20多年，然后于1978年出版。它正式阐明了社会网络的机制，并探讨了这些机制的数学后果（包括连接程度）。这份手稿留下了许多关于网络的重要问题没有解决，其中之一就是实际社会网络中的分离度数量。米尔格拉姆从巴黎回来后接受了这一挑战，导致在大众科学杂志《今日心理学》（Psychology Today）上的《小世界问题》（The Small World Problem）[8]中报道了这些实验，两年后在《社会测量学》（Sociometry）上出现了该论文更严格的版本。<ref name=":4" />《今日心理学》的文章为这些实验带来了巨大的宣传，在许多形成性工作被遗忘很久后，这些实验今天仍然广为人知。

米尔格拉姆Milgram在美国马萨诸塞州剑桥市的哈佛大学继续进行古雷维奇的熟人网络实验。并且在20世纪50年代初在巴黎大学访问，与科琴Kochen和德索拉-波尔de Sola Pool合作了手稿《接触与影响''Contacts and Influences''》<ref name=":3" />。他们未发表的手稿在学术界流传了20多年，然后于1978年出版。正式阐明了社会网络的机制，并探讨了这些机制的数学后果（包括连接程度）。这份手稿留下了许多关于网络的重要问题没有解决，其中之一就是实际社会网络中的分离度数量。米尔格拉姆从巴黎回来后接受了这一挑战，并且在大众科学杂志《今日心理学Psychology Today》上的《小世界问题The Small World Problem》 <ref name="Stanley Milgram 1968" /> 中报道了这些实验，两年后在《社会测量学Sociometry》上出现了该论文更严格的版本。<ref name=":4" />《今日心理学''Psychology Today'' 》的文章为这些实验带来了巨大的宣传，在许多形成性工作被遗忘很久后，这些实验今天仍然广为人知。

 

Milgram's article made famous<ref name="Stanley Milgram 1968" /> his 1967 set of experiments to investigate de Sola Pool and Kochen's "small world problem." Mathematician [[Benoit Mandelbrot]], born in [[Warsaw]], growing up in [[Poland]] then [[France]], was aware of the Statist [[rule of thumb]], and was also a colleague of de Sola Pool, Kochen and Milgram at the University of Paris during the early 1950s (Kochen brought Mandelbrot to work at the Institute for Advanced Study and later IBM in the U.S.). This circle of researchers was fascinated by the interconnectedness and "social capital" of human networks. Milgram's study results showed that people in the [[United States]] seemed to be connected by approximately three friendship links, on average, without speculating on global linkages; he never actually used the term "six degrees of separation." Since the ''Psychology Today'' article gave the experiments wide publicity, Milgram, Kochen, and [[Karinthy]] all had been incorrectly attributed as the origin of the notion of six degrees; the most likely popularizer of the term "six degrees of separation" would be [[John Guare]], who attributed the value '6' to [[Guglielmo Marconi|Marconi]].<ref name=SDS-R-01>{{cite web |url=http://www.aaa.si.edu/exhibitions/peggy-bacon|title= The concept of Six degrees of separation stretches back to Italian inventor Guglielmo Marconi |accessdate=16 July 2012 }}</ref>

Milgram's article made famous<ref name="Stanley Milgram 1968" /> his 1967 set of experiments to investigate de Sola Pool and Kochen's "small world problem." Mathematician [[Benoit Mandelbrot]], born in [[Warsaw]], growing up in [[Poland]] then [[France]], was aware of the Statist [[rule of thumb]], and was also a colleague of de Sola Pool, Kochen and Milgram at the University of Paris during the early 1950s (Kochen brought Mandelbrot to work at the Institute for Advanced Study and later IBM in the U.S.). This circle of researchers was fascinated by the interconnectedness and "social capital" of human networks. Milgram's study results showed that people in the [[United States]] seemed to be connected by approximately three friendship links, on average, without speculating on global linkages; he never actually used the term "six degrees of separation." Since the ''Psychology Today'' article gave the experiments wide publicity, Milgram, Kochen, and [[Karinthy]] all had been incorrectly attributed as the origin of the notion of six degrees; the most likely popularizer of the term "six degrees of separation" would be [[John Guare]], who attributed the value '6' to [[Guglielmo Marconi|Marconi]].<ref name=SDS-R-01>{{cite web |url=http://www.aaa.si.edu/exhibitions/peggy-bacon|title= The concept of Six degrees of separation stretches back to Italian inventor Guglielmo Marconi |accessdate=16 July 2012 }}</ref>

米尔格拉姆的文章使他在1967年为研究德-索拉-波尔和科亨的 "小世界问题 "而进行的一组实验变得有名<ref name="Stanley Milgram 1968" />。数学家Benoit Mandelbrot出生于华沙，在波兰和法国长大，他知道统计学家的经验法则，也是de Sola Pool、Kochen和Milgram在50年代初在巴黎大学的同事（Kochen把Mandelbrot带到高级研究所和后来在美国的IBM工作）。这个研究圈子对人类网络的相互关联性和 "社会资本 "非常着迷。米尔格拉姆的研究结果显示，在美国，人们似乎平均有大约三个友谊联系，而没有推测全球联系；他实际上从未使用过 "六度分隔 "一词。由于《今日心理学》的文章对这些实验进行了广泛的宣传，米尔格拉姆、科亨和卡林西都被错误地归结为六度概念的起源；"六度分隔 "一词最有可能的普及者是约翰-瓜雷，他将 "6 "这个数值归结为马可尼<ref name="SDS-R-01" />。

米尔格拉姆在1967年与 de Sola Pool 和 Kochen 研究的 "小世界问题 "而进行的一组实验变得有名<ref name="Stanley Milgram 1968" />。数学家Benoit Mandelbrot出生于华沙，在波兰和法国长大，他知道统计学家的经验法则，也是de Sola Pool、Kochen和Milgram在50年代初在巴黎大学的同事（Kochen把Mandelbrot带到高级研究所和后来在美国的IBM工作）。这个研究圈子对人类网络的相互关联性和 "社会资本 "非常着迷。米尔格拉姆的研究结果显示，在美国，人们似乎平均有大约三个友谊联系，而没有推测全球联系。其实他实际上从未使用过 "'''六度分隔''' "一词。由于《今日心理学》的文章对这些实验进行了广泛的宣传，使得米尔格拉姆、科亨和卡林西都被错误地认为是六度分离这个概念的的起源。说到"六度分隔 "一词最有可能的普及者是约翰-瓜雷 [[John Guare]]，他将 "6 "这个数值归结为马可尼 [[Guglielmo Marconi|Marconi]].<ref name="SDS-R-01" />。

In 2003, [[Columbia University]] conducted an analogous experiment on social connectedness amongst Internet email users. Their effort was named the Columbia Small World Project, and included 24,163 e-mail chains, aimed at 18 targets from 13 countries.<ref name="dodds">Dodds, Muhamad, Watts (2003)."Small World Project," Science Magazine. pp.827-829, 8 August 2003 https://www.sciencemag.org/content/301/5634/827</ref> Almost 100,000 people registered, but only 384 (0.4%) reached the final target. Amongst the successful chains, while shorter lengths were more common some reached their target after only 7, 8, 9 or 10 steps. Dodds et al. noted that participants (all of whom volunteers) were strongly biased towards existing models of Internet users{{#tag:ref|"More than half of all participants resided in North America and were middle class, professional, college educated, and Christian, reflecting commonly held notions of the Internet-using population"<ref name="dodds"/>|group=Note}} and that connectedness based on professional ties was much stronger than those within families or friendships. The authors cite "lack of interest" as the predominating factor in the high attrition rate,{{#tag:ref|"suggesting lack of interest ... was the main reason" for the "extremely low completion rate"<ref name="dodds"/>|group=Note}} a finding consistent with earlier studies.<ref name="kleinfeld">{{cite web|url=http://www.stat.cmu.edu/~fienberg/Stat36-835/Kleinfeld_SWP.pdf|title=The Small World Problem|publisher=[[Society (journal)|Society (Springer)]], Social Science and Public Policy|author=[[Judith Kleinfeld|Judith S. Kleinfeld]], [[University of Alaska Fairbanks]]|date=January–February 2002}}</ref>

In 2003, [[Columbia University]] conducted an analogous experiment on social connectedness amongst Internet email users. Their effort was named the Columbia Small World Project, and included 24,163 e-mail chains, aimed at 18 targets from 13 countries.<ref name="dodds">Dodds, Muhamad, Watts (2003)."Small World Project," Science Magazine. pp.827-829, 8 August 2003 https://www.sciencemag.org/content/301/5634/827</ref> Almost 100,000 people registered, but only 384 (0.4%) reached the final target. Amongst the successful chains, while shorter lengths were more common some reached their target after only 7, 8, 9 or 10 steps. Dodds et al. noted that participants (all of whom volunteers) were strongly biased towards existing models of Internet users{{#tag:ref|"More than half of all participants resided in North America and were middle class, professional, college educated, and Christian, reflecting commonly held notions of the Internet-using population"<ref name="dodds"/>|group=Note}} and that connectedness based on professional ties was much stronger than those within families or friendships. The authors cite "lack of interest" as the predominating factor in the high attrition rate,{{#tag:ref|"suggesting lack of interest ... was the main reason" for the "extremely low completion rate"<ref name="dodds"/>|group=Note}} a finding consistent with earlier studies.<ref name="kleinfeld">{{cite web|url=http://www.stat.cmu.edu/~fienberg/Stat36-835/Kleinfeld_SWP.pdf|title=The Small World Problem|publisher=[[Society (journal)|Society (Springer)]], Social Science and Public Policy|author=[[Judith Kleinfeld|Judith S. Kleinfeld]], [[University of Alaska Fairbanks]]|date=January–February 2002}}</ref>

2003年，哥伦比亚大学对互联网电子邮件用户的社会联系进行了类似的实验。他们的努力被命名为 "哥伦比亚小世界项目"，包括24,163条电子邮件链，目标是13个国家的18个目标。<ref name="dodds" />几乎有10万人注册，但只有384人（0.4%）达到了最终目标。在成功的邮件链中，虽然长度较短的邮件链比较常见，但有些邮件链只经过7、8、9或10步就达到了目标。Dodds等人指出，参与者（他们都是志愿者）强烈地偏向于现有的互联网用户模式，基于职业关系的联系要比家庭或朋友关系中的联系强得多。作者指出，"缺乏兴趣 "是造成高流失率的主要因素，这一发现与早期研究一致。<ref name="kleinfeld" />

2003年，哥伦比亚大学对互联网电子邮件用户的社会联系进行了类似的实验。他们的工作被命名为 "哥伦比亚小世界项目"，包括24,163条电子邮件链，目标是涵盖13个国家的18个目标。<ref name="dodds" />几乎有10万人注册，但只有384人（0.4%）达到了最终目标。在成功的邮件链中，虽然长度较短的邮件链比较常见，但有些邮件链只经过7、8、9或10步就达到了目标。Dodds等人指出，参与者（他们都是志愿者）强烈地偏向于现有的互联网用户模式，基于职业关系的联系要比家庭或朋友关系中的联系强得多。作者指出，"缺乏兴趣 "是造成高流失率的主要因素，这一发现与早期研究一致。<ref name="kleinfeld" />