Introduction

As the discussion in Chapter 6 shows, minor variations in the technical specifications of different voting systems can have a major impact on their relative performance. In the same way, ‘second tier’ electoral system design choices, such as the number of members elected from each district or the layout and structure of the ballot, can significantly affect the efficacy of different systems as instruments of constitutional engineering. Two particularly important alternatives when implementing preferential voting systems are the choice between single-member versus multi-member electoral districts, and the alternatives of making the marking of preferences a legal requirement for a valid ballot or leaving the decision to mark preferences in the hands of the voter. I will argue in this chapter that such apparently trivial decisions can have major implications for the success or failure of centripetal strategies.

In his seminal work on the political consequences of electoral laws, Douglas Rae (1967, 16–39) argued that there are three crucial sources of variation between different electoral systems:

1. Electoral formula – that is, the method by which votes cast are translated into seats won, e.g. choices between majoritarian formulae such as FPTP, AV, SV and run-off systems; semi-proportional formulae such as parallel systems or the single non-transferable vote; and forms of proportional representation such as list PR or STV.

2. […]