I'm interested in any research materials on voting patterns.
I have a data set of how PMs (members of parliament) voted in my country during last couple of years. Each PM has 3 buttons: Yes, No, Abstain. There are also two special situations: PM can be absent during the voting and he/she can be present but not vote (it's wrong but they do it sometimes). So any particular voting result is represented as a huge vector whose values are yes/no/abstain/present_not_voted/absent.
I'd like to find some similarities in PMs' voting patterns and cluster them in groups based on these similarities. There are some interesting questions like coalition stability and party loyalty which (in theory) could be answered with the data described above. Unfortunately i deeply lack any references.
While googling i've come across some site which formed an undirected graph based on American senators voting. It looked cool but i didn't find any explanation on how such graph can be formed. Intuitively "similar" is a symmetric binary relation so undirected graph representation sounds quite natural. But how can one define "similarity" for my data? Probably there are some standard ways of doing this. Any help will be highly appreciated.