The following pages explain the details of how we calculate the Legislative Power Share scores for Canada and the three comparator countries that use proportional voting systems that we have evaluated: List PR (Norway), MMP (New Zealand) and STV (Ireland).
For all of the comparator countries, the calculations are designed to measure fundamentally the same quantity as for First Past the Post - namely, what share an individual voter has of legislative influence relative to a situation of parity in which all voters have equal shares of legislative influence. In all cases, a voter is considered to have a share of legislative power only if their vote is counted towards the election of one or more representatives; otherwise, a voter is considered to have an LPS score of zero.
While small adjustments have been made to accommodate limitations in the data available, we have been able to apply substantially the same concept to all four systems, so the resulting LPS score distributions and the associated Legislative Power Disparity Indices should be considered to be directly comparable across systems.
These calculations, as explained in the subsequent pages, result Legislative Power Share scores distributed as shown in the following graph: