Electoral Threshold of Proportional Representations Systems, Theory and Reality

The main purpose of this paper is to briefly introduce the broad field of electoral threshold. The poper focuses only on the thresholds of proportional representation systems. This topic is practically unknown in Czech political science literature. Electoral threshold is very important for electoral studies, because it strongly affects representation of small parties. The first part describes theoretical computational methods of effective threshold at district level. The effective threshold depends on the threshold of inclusion and the threshold of exclusion. They are, respectively, the vote shares below which a party cannot possibly win a seat, and above which it cannot possible fail to do so. There is not a consensus above computational methods of threshold of inclusion. Therefore, we distinguish three possibilities how to count dependent values of effective threshold. The second part shows theoretical computational methods of the average threshold at national level. It is connected witch the threshold of inclusion and the threshold of exclusion at national level. It is important to keep in mind, that every theoretical pattern gives only approximate results. We can count really values of electoral thresholds of concrete election results by the practical methods described at the third part. We distinguish methods for systems using electoral quotas and for systems using electoral divisors. Computational methods of real values of electoral threshold (practical methods) give more exact results those theoretical methods, which give only appropriate values. On the other hand, practical methods need much more incoming information and their results could not possibly be as general as theoretical methods.