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6. The total alter effect, expressing that actors whose alters have a higher total value
of the behavior Z, also have themselves a stronger tendency toward high values on
the behavior.
7. The indegree effect, expressing that actors with a higher indegree (more ‘popular’
actors) have a stronger tendency toward high values on the behavior.
8. The outdegree effect, expressing that actors with a higher outdegree (more ‘active’
actors) have a stronger tendency toward high values on the behavior.
Effects 1 and 2 will practically always have to be included as control variables. (For
dependent behavior variables with 2 categories, this applies only to effect 1.) When the
behavior dynamics is not smooth over the observation waves — meaning that the pattern
of steps up and down, as reported in the initial part of the output file under the heading
Initial data description – Dependent actor variables – Changes, is very irregular across
the observation periods — it can be important to include effects of time variables on the
behavior. Time variables are changing actor covariates that depend only on the observation
number and not on the actors. E.g., they could be dummy variables, being 1 for one or
some observations, and 0 for the other observations.
The average similarity, total similarity, average alter, and total effects are different
specifications of social influence. The choice between them will be made on theoretical
grounds and/or on the basis of statistical significance. Do not include them all together
in one model, as this would most likely lead to multicollinearity and non-convergence.
For each actor-dependent covariate as well as for each of the other dependent behavior
variables, the effects on Z which can be included is the following.
1. The main effect: a positive value implies that actors with a higher value on the
covariate will have a stronger tendency toward high Z values.
2. Various effects of the combination of covariate values for members of the personal
network of the focal actor (outgoing ties, incoming ties, distance-two ties): search
in this manual for avXAlt, avXInAlt, avXAltDist2, avXInAltDist2 and their
manifold variations.
3. Interactions between two or three actor variables, see Section 5.8.
5.7
Model Type: non-directed networks
Non-directed networks are an undocumented option (there currently only is the presentation Snijders (2007).
SIENA detects automatically when the networks all are non-directed, and then employs
a model for this special case. For non-directed networks, the Model Type has five possible
values, as described in Snijders (2007). This is specified by the parameter modelType in
function sienaAlgorithmCreate. Value modelType = 1 is for directed networks, values 2-6
for non-directed networks.
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