  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.
