Abstract
ABSTRACTHow proportional are the results of electoral systems designed to ensure proportional representation? How large is the deviation from proportionality for relative majority systems? Does a given system favor large, small or medium‐sized parties? Are some parties consistently advantaged? Is the system predictable or erratic? Plotting the percentage of seats–percentage of votes ratio versus percentage of votes for all parties, is found to be a simple and yet powerful graphical method to answer such questions. Application of such “proportionality profiles” to West European multi‐party systems leads to a typology of electoral systems based on their actual effect (rather than their formal procedure or intended effect). District magnitude, the number of rounds, and nationwide adjustment rules are found to be more important than formal seat distribution rules such as d'Hondt or Sainte‐Laguë.
Highlights
Theoretical analysis of electoral laws has cast some light on the effects of the different systems of proportional representation
The perfect proportionality line ( A = 1) is shown on all our proportionality profile plots. We have found it useful to show the vertical %V = 10% line because this line delimits the region where small-party disadvantage tends to change into large-party advantage, for many electoral systems
We considered omitting the “Other Parties” category from our profiles, but that may distort the picture
Summary
Theoretical analysis of electoral laws has cast some light on the effects of the different systems of proportional representation. Fractionalization and the effective number of parties usually decrease in the process of translating votes into assembly seats, indicating that minor parties tend to be eliminated or under-represented, Plotting seat shares versus vote shares shows that even the supposedly proportional electoral systems tend to favor larger parties at the expense of the smaller ones (Rae, 1967). The differences between the vote and seat shares for individual parties can be summed up t o express the deviation from proportionality for a given election Before we can locate fruitful theoretical avenues and suitable approaches to supposedly empirical analysis we need a way t o present all elections results relevant for a given electoral system in a single picture that can be seen at a single glance in all its complexity.
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