[EM] Simulation of Duverger's Law

[James Gilmour]

Raph Frank  > Sent: Thursday, October 16, 2008 11:04 AM
> > On Thu, Oct 16, 2008 at 6:46 AM, Greg Nisbet 
> > Why doesn't France's Two Round System lead to the same result?
> 
> It could be argued that the first round is somewhat random.  

If you are going to simulate Duverger's so-called "law", your model would have to accommodate what has actually happened in the UK
with plurality (FPTP) elections in single-winner electoral districts.  Contrary to all the predictions from the "law", the
percentage of votes in UK general elections for the two largest parties has declined from 97% in 1951 to 68% in 2005 (most recent).
During this time there have been around 650 seats (MPs) in the House of Commons (lower house of the UK Parliament, and seat of the
Government).  In the 2005 general election the votes for the three largest parties were: 35%, 32%, 22%.

These changes are shown in the graph available at:	
  http://www.jamesgilmour.f2s.com/Percentage-Votes-for-Two-Largest-Parties-UK-GEs-1945-2005.pdf	
or	
  http://www.jamesgilmour.org.uk/Percentage-Votes-for-Two-Largest-Parties-UK-GEs-1945-2005.pdf


During the same period, within Scotland, which elected 72 of those MPs by FPTP in single-member electoral districts, the number of
significant parties (in terms of votes) increased from two to three and then from three to the current four.

James Gilmour
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