MEASURING PARLIAMENTARY DEVIATION

Deviation between party seat shares and party expected power in parlia mentary winning coalitions is measured with a new formula. In analogy with electoral deviation, in which proportions of votes and proportion s of seats for each party are compared, proportions of seats and the p roportions of influence in parliamentary majorities for each party are compared. A new parliamentary power index, which can be applied to di fferent criteria in coalition formation, is used for this purpose. For mal trends of parliamentary disporportionality are presented. An empir ical application for real elections in the period 1972-1993 in five Eu ropean countries with parliamentary regimes shows a positive correlati on between electoral deviation and parliamentary deviation.