calculating centrality

Nov 11, 2008 at 1:56 PM
Is there a way to calculate centrality? I know some other programs allow you to calculate it and was hoping .NetMap had a way to do it as well.
Nov 11, 2008 at 4:57 PM
Maureen:

The only graph metrics we calculate right now are listed under .NetMap, Analysis, Calculate Graph Metrics-down-arrow, Select Graph Metrics.  They include betweeness centrality, but not other types of centrality.

However, we've been asking users which other metrics would be most useful to add to .NetMap.  Did you have a particular type of centrality in mind?  I see there are several:

http://en.wikipedia.org/wiki/Centrality

-- Tony
Nov 11, 2008 at 5:23 PM
The measures of centrality I've seen being used (I'm still learning) are; closeness, degree, information, and eigenvector. I believe these are the main ones that were mentioned at a workshop for Networks in Political Science workshop last summer.

on a different question (as I'm still learning) I am confused about a couple things, first, is there a way to just show part of the network? for example I have 158 cases and states that are linked to them yielding over 1400 links in the network- if I wanted to look at just one or two cases and those connections is there an easy way to do this? second, is there a way to manipulate the subgraphs in the vertices tab? (i.e. make them bigger or figure out what these subgraphs mean)
Nov 11, 2008 at 5:52 PM
There are several ways to show part of a network.  First, if you want full control of the visibility of every edge and vertex, you can use the Visibility columns on the Edges and Vertices worksheets.  Hover over the "How Edge Visibility Works" and "How Vertex Visibility Works" cells for details.

That's probably too difficult for a large graph, though.  Here is an easy way to show just one or two cases:

1. Click Options in the graph pane, and set Edges Opacity and Vertices Opacity to zero.  Click OK.  Everything in the graph will disappear.

2. In the Vertices worksheet, select a vertex.  Selected vertices and edges are always visible regardless of the Options settings, so your selected vertex and its incident edges are now the only things shown in the graph.

3. You can control-click in the worksheets to select additional vertices and edges, and you can right-click a vertex or edge in the worksheet and select .NetMap from the context menu to get even more control of what's selected (and therefore what's visible).  You can also right-click a vertex in the graph pane for selection options.

You could also use dynamic filters to filter out most of the graph if you have some numeric column that could serve as an effective filter.

The next version of .NetMap, which I'm working on now, has an "Export Selection to New Workbook" ribbon command that will pull out selected vertices and edges and write them to a new workbook, so you might be interested in that when it's released.

On your second question, the Create Subgraph Images dialog box has options for setting the size of the thumbnail images that get inserted into the Vertices worksheet, and a few other things, too.  You can also save the images to disk.  Figuring out what they mean is up to you, though; we merely create pretty pictures.

-- Tony
Nov 11, 2008 at 7:00 PM
Another kind of important measure of centrality is actor centrality I found it used in Wasserman and Faust 1994 which describes the math behind it all