The authority score for a node measures the tendency of other nodes in the group to connect to it. If many individuals are contacting a particular person, potentially asking for information or opinions, that person has the role of an authority. The authority scores for the nodes in group, which correspond to the stationary probabilities for a random walk with restarts through the group network, range from 0 to 1. The closer the authority score is to 1, the more authority that node has within the group. The node in the group with the highest authority score is referred to as the authority leader for the group. Dividing the largest score within a group by the smallest provides a measure of the overall strength of the authority leader.
In contrast, the dissemination score for a node measures the tendency of the node to connect to other nodes in the group. If a particular person contacts many other people in the group, that person can significantly affect the opinions of the entire group. The dissemination scores for the nodes in group, which correspond to the stationary probabilities for a random walk with restarts
through the group network in reverse, range from 0 to 1. The closer the dissemination score is to 1, the more the node connects to the other group members. The node in the group with the highest dissemination score is referred to as
the dissemination leader for the group. Dividing the largest score within a group by the smallest provides a measure of the overall strength of the dissemination leader.
SPSS do provide an Modlerler 15.0 Algorithm Guide, but unfotunately I have not found anything about SNA from it.
ftp://public.dhe.ibm.com/software/analytics/spss/documentation/modeler/15.0/en/AlgorithmsGuide.pdf