NATIONWIDE INCLUSION AND EXCLUSION THRESHOLDS OF REPRESENTATION

The theoretical inclusion and exclusion thresholds are, respectively, the vote shares below which a party cannot possibly win a seat, and ab ove which it cannot possibly fail to do so. They are important in eval uating how hospitable electoral systems are to small parties. Previous ly, they have been calculated at the district level. Here the theory i s extended to the national level. Surprisingly, the inclusion threshol d depends on the smallest district in the country - not the largest. T he exclusion threshold depends on all districts. The theoretical resul ts are compared to empirical observations for 23 electoral systems. Th e inclusion threshold is indeed close to the minimal vote share that e ver led to a seat in the national assembly. In stark contrast, the exc lusion threshold is much higher than the maximal vote share that ever failed to produce a seat in practice. The total number of districts em erges as a significant variable. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.