
Hi everybody!
I am new to SNA and to NodeXL. Today I started to work on a nodeXL file and I calculated the graphic metrics. Betweenness centrality had values very high like 330.00 and even more. Betweenness should be a value between 0 and 1, shouldn't it?
Do you know if I am doing anything wrong?
Thank you very much!



You are not doing anything wrong. Betweenness centralities are between 0 and 1 only if they are normalized, and NodeXL does not normalize them. We decided not to normalize them because the absolute numbers have meaning that some people find useful.
If you need normalized values, you can add a new column to your Vertices worksheet, then use an Excel formula to normalize the values from the Betweenness Centrality column. The rules for normalization can be found here:
http://en.wikipedia.org/wiki/Centrality#Betweenness_centrality
The Excel formula for normalization within a directed graph, for example, would look like this, assuming the graph has at least 3 vertices:
=Vertices[ [#This Row],[Betweenness Centrality] ] / ( (COUNT( [Betweenness Centrality] )  1) * (COUNT( [Betweenness Centrality] )  2) )
 Tony



Thank you very much for your reply. It is clear now. I tried to make ii normalized but it doesn't seem to work probably because I am doing something wrong with the formula. Do you have any sample on a file that could make it more clear?
Thank you so much!


Sep 3, 2010 at 5:33 PM
Edited Sep 3, 2010 at 5:45 PM

I do have a sample file, but CodePlex doesn't allow files to be posted in its discussions. Stepbystep instructions might be better anyway, because they might help others who run into the same problem. Skip to step 5 for the quick solution to
your problem.
1. To calculate betweenness centrality, go to NodeXL, Analysis, Graph Metrics in the Excel ribbon, check "Betweenness and closeness centralities" in the Graph Metrics dialog box, and click Calculate Metrics. That will automatically switch
you to the Vertices worksheet with the newly calculated centralities showing.
2. Select the Closeness Centrality column, rightclick, and select Insert. That inserts a column to the right of Betweenness Centrality. Change the new column's name to Normalized Betweenness Centrality.
3. Copy the following formula to the clipboard:
=Vertices[ [#This Row],[Betweenness Centrality] ] / ( (COUNT( [Betweenness Centrality] )  1) * (COUNT( [Betweenness Centrality] )  2) )
4. Select the first empty cell in the Normalized Betweenness Centrality column.
5. In the Excel ribbon, select Home, Clipboard, Paste, Paste Special. In the Paste Special dialog box, select Unicode Text, then click OK.
If, in step 5, you just do a simple Paste, you will be pasting "HTML" instead of text, and the formula won't work.
The formula will fail if your graph doesn't have at least two vertices. The formula can be adjusted to handle that, but I haven't bothered with that here.
 Tony

