The changing local political landscape: Fragmentation and coalition formation in the Netherlands (1998-2022)

Using data for Dutch municipal elections in almost all Dutch municipalities between 1998 and 2022, this paper investigates how political fragmentation and coalition formation develops. We calculate two fragmentation indexes. Firstly, we measure fragmentation by the (absolute) number of political parties in the council and board. Secondly, we include the relative size of parties and in allowing for differences in the relative size of parties, the effective number of political parties can be calculated. Moreover, we calculate conversion ratios that divide the share of aldermen by the share of council seats for each political party. For independent local parties, we see the ratio is increasing and getting closer to one. Interestingly, if we distinguish between for example local protest parties and localistic parties, this conversion ratio is substantially below one for protest and above one for localistic parties. Finally, the presence of representative coalitions is investigated based on an operational definition as worked out by Tops (1990). We show that the number of municipalities with a representative coalition is decreasing over time in the strict and weak sense.