This is an excellent summary of selectorate theory, but on parliamentary versus presidential systems there’s an important distinction that gets lost in translation from the academic work. The post conflates parliamentary systems with single-member constituencies (like the UK) with those using proportional representation (like Israel), particularly when discussing coalition sizes.
The original authors acknowledge this limitation in their academic work whenever they distinguish between parliamentary and presidential systems, but this nuance isn’t captured here. The UK’s parliamentary system can produce governments with large majorities on 35% of votes, creating a smaller effective winning coalition. Israel’s PR system requires genuine majority support (among the enfranchised at least). Parliamentary systems with PR tend towards broader coalitions and different dynamics than those with single-member constituencies, despite both being “parliamentary”, and the difference disappears when you correct for these.
Thanks for the comment! You’re correct, I did miss that when writing the post. They do mention in their work that there should be a difference between different parliamentary systems (though the empirical work they’ve done at the time of the book’s publication didn’t differentiate between them). I most places they don’t clearly say which one should have a large coalition size, like in this part (emphasis mine):
Not all competitive electoral systems are alike in the required size of the winning coalition. First-past-the-post parliamentary systems, for instance, require a winning coalition equal to only about one-quarter or less of the selectorate. If such a system has only two political parties and the prime minister requires support from half of the legislators in order to remain in power, and each legislator needs approximately a simple majority to be elected, then the prime minister needs support from one-half of the legislators, each of whom needed support from one-half of his or her constituents in order to be elected. Thus the prime minister only needs support from one-fourth of the voters. If there are more than two viable political parties, then the prime minister needs an even smaller percentage of the selectorate in order to remain in power. In many proportional-representation systems the size of the winning coalition can be substantially smaller than one-quarter.
This makes it sound like proportional representation is worse than FPTP/Single Member Districtrs.
but in one of the notes they do state it clearly:
we expect list-voting parliamentary systems to behave in a manner similar to direct-election presidential systems, but we anticipate that winner-take-all, single-member district parliamentary systems behave in a manner consistent with regimes that have a smaller winning coalition than do presidential systems or list systems.
This is an excellent summary of selectorate theory, but on parliamentary versus presidential systems there’s an important distinction that gets lost in translation from the academic work. The post conflates parliamentary systems with single-member constituencies (like the UK) with those using proportional representation (like Israel), particularly when discussing coalition sizes.
The original authors acknowledge this limitation in their academic work whenever they distinguish between parliamentary and presidential systems, but this nuance isn’t captured here. The UK’s parliamentary system can produce governments with large majorities on 35% of votes, creating a smaller effective winning coalition. Israel’s PR system requires genuine majority support (among the enfranchised at least). Parliamentary systems with PR tend towards broader coalitions and different dynamics than those with single-member constituencies, despite both being “parliamentary”, and the difference disappears when you correct for these.
Thanks for the comment! You’re correct, I did miss that when writing the post. They do mention in their work that there should be a difference between different parliamentary systems (though the empirical work they’ve done at the time of the book’s publication didn’t differentiate between them). I most places they don’t clearly say which one should have a large coalition size, like in this part (emphasis mine):
This makes it sound like proportional representation is worse than FPTP/Single Member Districtrs.
but in one of the notes they do state it clearly:
I added an explanation of this to the Presidential VS Parliamentary Democracy section. Thanks!