Thursday, April 05, 2007

The 'bozza Chiti' and the effective threshold

From comes information on the size of constituencies in the new electoral system proposed in the 'bozza Chiti'. They will be 'sub-provinciale', at most, 'provinciale'.

Let's assume conservatively that the constituencies will be equal to the number of provinces.

Let's also assume, as a simplifying measure, that the constituencies will all be given the same number of members of parliament to elect.

So, dividing the number of parliamentarians in the bozza Chiti - 400 - by 103, we get 3.88 MPs to be elected per constituency.

The effective threshold per constituency is therefore: 75% / (3.88 + 1) = 15.36%.

Now, the effective threshold at the constituency level is not a good estimate of the effective threshold at national level. Rein Taagepeera, in a 2002 Electoral Studies article, suggests that the nationwide threshold is equal to:

  • effective constituency threshold / (square root of number of districts), or
  • 15.36 / 1o3 ^ 0.5 = 15.36 / 10.15 = 1.51%
So, if anything, the proposed system is going to present a less formidable barrier to parties than the previous system, which had a legal threshold of 2% (plus largest coalition loser). Admittedly, these are back of the envelope calculations, and the distribution of seats between constituencies may (significantly) affect the results. But, if a (more) reductive electoral system is a good thing for Italy, then we'd better hope that the constituencies are more numerous than the one hundred and three provinces.

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