The way in which an electoral system influences the party system is a salient topic discussed in political science and social choice theory. Researches in post-communist countries have so far usually been analyses of the isolated cases of the elections. Here all free parliamentary elections in this region are examined. It allows measuring the total effect of the electoral system on the party system. It was found that the consequences of some electoral institutions are different than observed in old democracies: single-member districts with majority rule may cause considerable parliament fragmentation and the consequences of mixed systems are heterogeneous and depending on their inner mechanics. It was also found that the form of the party system depends to a greater degree on the properties of the political scene than on the electoral system.

In this work we analyze the methods commonly used for support the pre-negotiation activities, that negotiators undertake to prepare well to thenegotiation process. We discuss the additive scoring model (AMS), mostfrequently used in pre-negotiation support for determining the scoring system of the negotiation offers and show the empirical example of applying such a model in pre-negotiation preparation. We also discuss the assumptions that make this model legitimate and consider its limitations. The recent empirical works describing how negotiators behave in electronic negotiation show however, that some negotiators should not be supported with AMS. Therefore we propose two alternative tools that can be used in pre-negotiation support alternatively. The first one basis on the ELECTRE-TRI method and allows to determine the negotiation offers' scoring system without the direct assigning the scoring points to negotiation issues and options. The second one applies the TOPSIS algorithm that needs to be modified and extended to fulfill the negotiation protocol requirements. For both the approaches we present the numerical examples showing how they can be applied in the pre-negotiation support.

The article presents and confronts empirically two popular conceptions explaining the phenomenon of comparative optimism: egocentric and focalistic ones. The results of two consecutive experiments unequivocally supported the validity of the focalistic conception. The studies proved that the reversal of the direction of comparison in such a way that subjects had to compare the situation of the generalized other with their own situation (instead of comparing their own situation with the situation of the generalized other) resulted in the reversal of well known relationship between the perceived frequency of eventsand the amount of comparative optimism, which increased altogether with theperceived frequency of negative events (Study 1) and decreased altogether with the perceived frequency of positive events (Study 2). This research is the first one in the literature showing such a pattern of results.