Within-country determinants of political party structures: Similarity-based analysis of Polish party statutes

We seek to explain within-country determinants of political party structures. However, unlike most scholars in the field, who start with hypotheses connecting specific structural features with specific explanatory variables (e.g., ideology, party age), we instead seek to explain overall structural similarity in terms of such variables. This allows us to determine whether the latter have an effect on party structures, even if we have no a priori hypotheses about what exactly this effect is. In the paper, we first introduce a new measure of structural similarity of political parties, based on their formal institutional arrangements reflected in their statutes. Then, using a dataset of Polish party statutes, and following the similarity-based hypothesis testing approach, we verify hypotheses about party structures being determined by ideology, party age, time of observation, as well as legislative and electoral experience of party candidates.