dunbar's number

Examples of dunbar's number in the following topics:

• Effects of Group Size on Stability and Intimacy

  • Facebook presents an interesting example of how modern technology may or may not impact Dunbar's number.
  • Intimate communities seldom have more than about 150 members, a number derived from the "Dunbar's Number" concept.
  • This is the suggested cognitive limit to the number of people with whom one can maintain stable social relationships.
  • Like animals, the number of relationships the human brain can handle is large but not unlimited .

• Networks

  • Research in a number of academic fields has demonstrated that social networks operate on many levels, from families up to the level of nations, and play a critical role in determining the way problems are solved, organizations are run, and the degree to which individuals succeed in achieving their goals.
  • The so-called rule of 150 states that the size of a genuine social network is limited to about 150 members (sometimes called the Dunbar Number).
  • It is theorized in evolutionary psychology that the number may be some kind of limit of average human ability to recognize members and track emotional facts about all members of a group.

• The Origins of Culture

  • Dunbar has proposed that language evolved as early humans began to live in large communities that required the use of complex communication to maintain social coherence.

• Introduction to connection

  • Focusing first on the network as a whole, one might be interested in the number of actors, the number of connections that are possible, and the number of connections that are actually present.
  • The number and kinds of ties that actors have are a basis for similarity or dissimilarity to other actors -- and hence to possible differentiation and stratification.
  • The number and kinds of ties that actors have are keys to determining how much their embeddedness in the network constrains their behavior, and the range of opportunities, influence, and power that they have.

• Introduction to closeness centrality

  • One actor might be tied to a large number of others, but those others might be rather disconnected from the network as a whole.
  • Depending on how one wants to think of what it means to be "close" to others, a number of slightly different measures can be defined.

• Krackhardt's Graph Theoretical Dimensions of Hierarchy

  • Krackhardt develops index numbers to assess the extent to which each of the four dimensions deviates from the pure ideal type of an out-tree, and hence develops four measures of the extent to which a given structure resembles the ideal typical hierarchy.
  • We can measure the extent to which this is not true by looking at the ratio of the number of pairs in the directed graph that are reachable relative to the number of ordered pairs.
  • We can assess the degree of deviation from pure hierarchy by counting the number of pairs that have reciprocated ties relative to the number of pairs where there is any tie; that is, what proportion of all tied pairs have reciprocated ties.
  • The amount of deviation from this aspect of the pure out-tree can be measured by counting the difference between the actual number of links (minus 1, since the ultimate boss has no boss) and the maximum possible number of links.
  • The deviation of a graph from this condition can be measured by counting the numbers of pairs of actors that do not have a common boss relative to the number of pairs that could (which depends on the number of actors and the span of control of the ultimate boss).

• Optimization by tabu search

  • Network>Roles & Positions>Exact>Optimization provides a numerical tool for finding the best approximations to a user-selected number of automorphism classes.
  • In using this method, it is important to explore a range of possible numbers of partitions (unless one has a prior theory about this), to determine how many partitions are useful.
  • Having selected a number of partitions, it is useful to re-run the algorithm a number of times to insure that a global, rather than local minimum has been found.
  • We ran the routine a number of times, requesting partitions into different numbers of classes.
  • In between, one might want to follow the logic of the "scree" plot from factor analysis to select a meaningful number of partitions.

• Fertility

  • There are a number of different ways, taking different factors into account, to measure fertility rate.
  • Crude birth rate (CBR) is the number of live births in a given year per 1,000 people alive at the middle of that year.
  • General fertility rate (GFR) is the number of births in a year divided by the number of women of childbearing age (usually 15 to 49 years old, or sometimes 15 to 44 years old), times 1000.
  • Child-Woman Ratio (CWR) is the ratio of the number of children under 5 to the number of women 15-49, times 1000.
  • Age-specific fertility rate (ASFR) is the number of births in a year to women in a 5-year age group, divided by the number of all women in that age group, times 1000.

• Walks etc.

  • The length of a walk is simply the number of relations contained in it.
  • The length of a trail is the number of relations in it.
  • In our example above, there are a number of trails from A to C.
  • In this directed graph, there are a number of walks from A to C.
  • Counts of the numbers of paths of various lengths are shown in figure 7.12.

• Factions

  • More commonly, we might use this tool in an exploratory way, examining the results from several runs with differing numbers of factions.
  • After running several alternative numbers of blocks, we settled on four as meaningful for our purposes.
  • The "Final number of errors" can be used as a measure of the "goodness of fit" of the "blocking" of the matrix.
  • This count (27 in this case) is the sum of the number of zeros within factions (where all the ties are supposed to be present in the ideal type) plus the number of ones in the non-diagonal blocks (ties between members of different factions, which are supposed to be absent in the ideal type).
  • The final panel of the results reports the "block densities" as the number of ties that are present in blocks as proportions of all possible ties.