We present a study of the network of relationships among elected members of the Finnish
parliament, based on a quantitative analysis of initiative co-signatures, and its evolution
over 16 years. To understand the structure of the parliament, we constructed a statistically
validated network of members, based on the similarity between the patterns of initiatives
they signed. We looked for communities within the network and characterized them in
terms of members’ attributes, such as electoral district and party. To gain insight on the
nested structure of communities, we constructed a hierarchical tree of members from the
correlation matrix. Afterwards, we studied parliament dynamics yearly, with a focus on
correlations within and between parties, by also distinguishing between government and
opposition. Finally, we investigated the role played by specific individuals, at a local level.
In particular, whether they act as proponents who gather consensus, or as signers. Our
results provide a quantitative background to current theories in political science. From a
methodological point of view, our network approach has proven able to highlight both local
and global features of a complex social system.