are selected by probability methods. The logic of the method treats each individual as a
separate "replication" that is, in a sense, interchangeable with any other.
Because network methods focus on relations among actors, actors cannot be sampled
independently to be included as observations. If one actor happens to be selected, then we
must also include all other actors to whom our ego has (or could have) ties. As a result,
network approaches tend to study whole populations by means of census, rather than by
sample (we will discuss a number of exceptions to this shortly, under the topic of
sampling ties).
The populations that network analysts study are remarkably diverse. At one extreme, they
might consist of symbols in texts or sounds in verbalizations; at the other extreme, nations in
the world system of states might constitute the population of nodes. Perhaps most common, of
course, are populations of individual persons. In each case, however, the elements of the
population to be studied are defined by falling within some boundary.
The boundaries of the populations studied by network analysts are of two main types. Probably
most commonly, the boundaries are those imposed or created by the actors themselves. All
the members of a classroom, organization, club, neighborhood, or community can constitute a
population. These are naturally occuring clusters, or networks. So, in a sense, social network
studies often draw the boundaries around a population that is known, a priori, to be a network.
Alternatively, a network analyst might take a more "demographic" or "ecological" approach to
defining population boundaries. We might draw observations by contacting all of the people
who are found in a bounded spatial area, or who meet some criterion (having gross family
incomes over $1,000,000 per year). Here, we might have reason to suspect that networks
exist, but the entity being studied is an abstract aggregation imposed by the investigator --
rather than a pattern of institutionalized social action that has been identified and labeled by it's
participants.
Network analysts can expand the boundaries of their studies by replicating populations. Rather
than studying one neighborhood, we can study several. This type of design (which could use
sampling methods to select populations) allows for replication and for testing of hypotheses by
comparing populations. A second, and equally important way that network studies expand their
scope is by the inclusion of multiple levels of analyis, or modalities.
Return to the table of contents of this page
Modality and levels of analysis
The network analyst tends to see individual people nested within networks of face-to-face
relations with other persons. Often these networks of interpersonal relations become "social
facts" and take on a life of their own. A family, for example, is a network of close relations
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