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Concept: Six degrees of separation


Social networks show striking structural regularities, and both theory and evidence suggest that networks may have facilitated the development of large-scale cooperation in humans. Here, we characterize the social networks of the Hadza, a population of hunter-gatherers in Tanzania. We show that Hadza networks have important properties also seen in modernized social networks, including a skewed degree distribution, degree assortativity, transitivity, reciprocity, geographic decay and homophily. We demonstrate that Hadza camps exhibit high between-group and low within-group variation in public goods game donations. Network ties are also more likely between people who give the same amount, and the similarity in cooperative behaviour extends up to two degrees of separation. Social distance appears to be as important as genetic relatedness and physical proximity in explaining assortativity in cooperation. Our results suggest that certain elements of social network structure may have been present at an early point in human history. Also, early humans may have formed ties with both kin and non-kin, based in part on their tendency to cooperate. Social networks may thus have contributed to the emergence of cooperation.

Concepts: Sociology, Networks, Social psychology, Social network, Human evolution, Network theory, Complex network, Six degrees of separation


Pottery is a mainstay of archaeological analysis worldwide. Often, high proportions of the pottery recovered from a given site are decorated in some manner. In northern Iroquoia, late pre-contact pottery and early contact decoration commonly occur on collars-thick bands of clay that encircle a pot and extend several centimeters down from the lip. These decorations constitute signals that conveyed information about a pot’s user(s). In southern Ontario the period A.D. 1350 to 1650 witnessed substantial changes in socio-political and settlement systems that included population movement, coalescence of formerly separate communities into large villages and towns, waxing and waning of regional strife, the formation of nations, and finally the development of three confederacies that each occupied distinct, constricted areas. Social network analysis demonstrates that signaling practices changed to reflect these regional patterns. Networks become more consolidated through time ultimately resulting in a “small world” network with small degrees of separation between sites reflecting the integration of communities within and between the three confederacies.

Concepts: Sociology, Social network, Pottery, Network theory, Clay, Porcelain, Six degrees of separation


Comparator choice has been found one major factor impacting on the overall evidence supporting clinical interventions. We performed social network analysis on trials on the prevention/management of caries/carious lesions, hypothesizing that certain comparators are proportionally over-investigated, and others under-investigated, and that comparisons within comparator classes are preferred over comparisons between classes. A systematic review of randomized controlled trials on the prevention/management of caries/existing carious lesions was carried out. All comparators were classified at each of three levels of granularity, becoming more detailed with each level; (a) degree of invasiveness (non-, micro- or invasive), (b) the specific non-invasive, micro-invasive or invasive approach, © the actual material or technique used. Social network analysis was used to evaluate trial networks. Searching electronic databases found 4,774 articles of which 765 were relevant and 605 were included. The networks for all levels were polygonal. There was a high degree of separation of comparisons in prevention versus management trials. Invasive comparators were tested most frequently (number of comparators: 611), mainly in management trials. Non-invasive comparators were tested next often (474), mainly in caries prevention. Micro-invasive strategies were tested next often (233), in both, prevention and management trials. On more granular levels, few interventions dominated the networks. Regardless of the level, the majority of trials compared within, not between classes. Prevention trials were mainly conducted in children (number of trials in adults/children/both: 37/241/11), while those on managing lesions were conducted in both children and adults (117/179/21). Comparator choice in cariology trials is driven by indication, and limits conclusions on the true comparative effectiveness of all strategies. There are a variety of comparators that have not been, but should be, compared to one another, which should be addressed by future trials. Factors underlying trialists' comparator choice need to be identified.

Concepts: Randomized controlled trial, Sociology, The Trial, Invasive, Invasiveness of surgical procedures, Social network, Network theory, Six degrees of separation


Social networks play an important role in our daily lives. However, social ties are rather elusive to quantify, especially for large groups of subjects over prolonged periods of time. In this work, we first propose a methodology for extracting social ties from long spatio-temporal data streams, where the subjects are 17,795 undergraduates from a university of China and the data streams are the 9,147,106 time-stamped RFID check-in records left behind by them during one academic year. By several metrics mentioned below, we then analyze the structure of the social network. Our results center around three main observations. First, we characterize the global structure of the network, and we confirm the small-world phenomenon on a global scale. Second, we find that the network shows clear community structure. And we observe that younger students at lower levels tend to form large communities, while students at higher levels mostly form smaller communities. Third, we characterize the assortativity patterns by studying the basic demographic and network properties of users. We observe clear degree assortativity on a global scale. Furthermore, we find a strong effect of grade and school on tie formation preference, but we do not find any strong region homophily. Our research may help us to elucidate the structural characteristics and the preference of the formation of social ties in college students' social network.

Concepts: Sociology, Networks, Social network, Network theory, Complex network, Mathematical sociology, Six degrees of separation, Social networks


Conventional wisdom has it that everyone on earth is on average only six steps away from knowing any other person through ‘a friend of a friend’. On a local level, however, many people experience that most of their acquaintances know each other. It is thus hard to imagine how such a highly clustered group could be so well connected to the rest of the world. In this paper, we investigate how co-authorship connects scholars in medical education and whether the six degrees of separation hypothesis also applies to the network of authors in the field.

Concepts: Earth, World, Six degrees of separation, Small world experiment, Six Degrees of Kevin Bacon