Structuring the set of MPs in Polish Parliament: A simple clustering exercise

The paper presents a simple exercise of application of cluster analysis to the set of voting data for the members of Polish Parliament of the previous term, which started in 1993. Each MP is characterized by the vector contai ning the specification of MP's behaviour during individual votings, disting uishing the following categories: "For", "Against", "Abstained", "Not voted ", and "Absent". The distances between the "MP descriptions" containing the thus defined categories of behaviour during votings (forming the matrix of dimensions: number of MPs x number of votings) constitute the basis for th e analytic procedure based upon clustering. We are looking for the clusters of similar MP descriptions which are, simultaneously, possibly different b etween clusters. The analysis performed does not account for the membership of the MPs in th e political groupings (parties and alliances) within the parliament, and on e of the main goals of the analysis is just to identify the degree of agree ment between the results of the cluster analysis and the membership in such groupings. This is done after the procedure of clustering has been perform ed. Another aspect being of interest in the analysis is dependence upon (se nsitivity to) the parametric definitions of distances with respect to the c ategories adopted in the description of voting (e.g., "is absence the same as not voting?"). The results of analysis are meant to show to what extent the actual behaviour of the MPs reflect their political membership and what are the actual relations (in terms of true behaviour) between political gr oupings represented in the parliament. The objective of the altogether modest study was two-fold: (1) to assess th e capacity of the (definite algorithms of) cluster analysis in identificati on of the group structure of attitudes expressed through voting behaviour, and, given that such a capacity exists, (2) to compare the structure obtain ed with the formal membership in the political organizations, and also, tho ugh only marginally, with the structure of the political scene assumed or p erceived in the mass media or through the political pronouncements.