This paper investigates the time series properties of partisanship for five political parties in Spain. It is found that pure fractional processes with a degree of integration, d, between 0.6 and 0.8 fit the time-series behaviour of aggregate opinion polls for mainstream parties quite well, whereas values of d in the range of 0.3 to 0.6 are obtained for opinion polls related to smaller regional parties. Those results are in agreement with theories of political allegiance based on aggregation of heterogeneous voters with different degrees of commitment and pragmatism. Further, those models are found to be useful in forecasting the results of the last general elections in Spain. As a further contribution, new econometric techniques for estimation and testing of ARFIMA model are used to provide the previous evidence.
