Parliamentary constituency boundary reviews and electoral bias: How important are variations in constituency size?

Parliamentary Affairs

Volumn 63, Issue 1, 2010, Pages 4-21

  Borisyuk, Galina ^a   Rallings, Colin ^a   Thrasher, Michael ^a   Johnston, Ron ^b  

^a UNIVERSITY OF PLYMOUTH   (United Kingdom)

^b UNIVERSITY OF BRISTOL   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 73849124113     PISSN: 00312290     EISSN: 14602482     Source Type: Journal    
DOI: 10.1093/pa/gsp016     Document Type: Article

References (27)

1. R. J. Johnston, D. J. Rossiter and C. J. Pattie, 'Disproportionality and Bias in the Result of the 2005 General Election in Great Britain: Evaluating the Electoral System's Impact', Journal of Elections, Public Opinion and Parties, 16, 2006, 37-54.
2. Ibid..
3. It even stimulated Lord Baker of Dorking - a former Conservative Home Secretary - to pilot a Parliamentary Constituencies (Amendment) Bill through the House of Lords (it was never debated in the Commons) in 2007 which would have both reduced the number of constituencies by 65, created a uniform electoral quota for the entire UK, and limited variations around the quota to no more than 5 per cent. The debates on this Bill (Hansard, House of Lords, 18 May 2007, Column 399) illustrate the belief that variations in constituency size contributed substantially to the anti-Conservative bias at the previous three elections. Many of the Bill's proposals became official Conservative party policy in 2009 (see, for example, Telegraph View, 12 April 2009: http://www.telegraph.co.uk/news/newstopics/ politics/conservative/5145102/ Conservatives-plan-to-cut-number-of-MPs-by-65.html).
4. For full details on the redistribution process see D. J. Rossiter, R. J. Johnston and C. J. Pattie, The Boundary Commissions: Redrawing the UK's Map of Parliamentary Constituencies, Manchester University Press, 1999.
5. D. T. Denver, C. Rallings and M. Thrasher, Media Guide to the New Scottish Westminster Parliamentary Constituencies, Local Government Chronicle Elections Centre, 2004.
6. As it happens, the new constituencies proposed by the Boundary Commission for Scotland - a reduction to 59 from the 72 used at the 2001 election - were in place in time for the 2005 election: only one - with an electorate close to the Scottish average - was won by the Conservatives.
7. Following each review estimates are made of how votes would have been distributed had the new constituencies been in place at the previous general election: see C. Rallings and M. Thrasher, Media Guide to the New Parliamentary Constituencies, Local Government Chronicle Elections Centre, 1997;
8. C. Rallings and M. Thrasher, Media Guide to the New Parliamentary Constituencies, Local Government Chronicle Elections Centre, 2007.
9. The rules are set out in full in Rossiter et al. The Boundary Commissions.
10. The Liberal party did propose a subdivision of the island into two constituencies at the time of the Third Periodic Review, but put its representation in six months late.
11. The Conservatives' proposal to gain much greater equality - at least at the time when the electoral data are collected - involves weakening the importance of nesting constituencies within local government areas plus removing the 'special considerations' and 'community ties' rules, but without much more frequent and quicker reviews they cannot reduce the impact of population change.
12. R. H. Brookes, 'The Analysis of Distorted Representation in Two-Party, Single-Member Elections', Political Science, 12, 1960, 158-67.
13. R. Mortimore, The Constituency Structure and the Boundary Commission: the Rules for the Redistribution of Seats and their Effect on the British Electoral System, 1950-1987. DPhil Thesis, University of Oxford, 1992;
14. D. J. Rossiter, R. J. Johnston and C. J. Pattie 'Integrating and Decomposing the Sources of Partisan Bias: Brookes' Method and the Impact of Redistricting in Great Britain', Electoral Studies, 18, 1999, 367-78 and 649-50.
15. Our initial attempts at constructing a method for measuring bias in a three-party system can be found in G. Borisyuk, R. Johnston, C. Rallings and M. Thrasher, 'Measuring Bias: Moving from two-party to three-party Elections', Electoral Studies, 27, 2008, 245-56.
16. A more detailed outline of the method used here may be found in G. Borisyuk, R. Johnston, C. Rallings and M. Thrasher, A Method for Measuring and Decomposing Electoral Bias for the Three-Party Case, Political Methodology Working Papers, 2008, available at http://polmeth.wustl.edu/ workingpapers.php?order=datedesc& title=2008&startdate=2008-01- 01&enddate=2008-12-31. It has not yet proved possible to devise a method for the four-party case that applies in parts of Great Britain.
17. In England at the 2005 general election, for example, Labour obtained one seat for every 28,111 votes that it won, whereas the ratios for the Conservatives and Liberal Democrats were 41,982 and 110,591, respectively.
18. Wasted votes are those cast for a party in constituencies where it loses, and thus make no contribution to the number of seats that it wins. Surplus votes are those in excess of the number needed to defeat its main opponent in seats that it wins - in effect, its majorities there.
19. With 20,000 electors in a constituency contested by only two parties, 10,001 votes are needed for victory; with 25,000 electors, 12,501 are needed. Thus in an area with 100,000 electors and five constituencies, a party with 50,005 votes would win five seats; if that area had only four constituencies, then it would win only four.
20. The logic for this is given by reworking the data in the previous example. In a constituency with 20,000 electors and a turnout of 90%, 9001 votes would be needed for victory; if turnout were 70%, then only 7001 would be needed.
21. Johnston et al., op. cit.
22. Borisyuk et al., op. cit.
23. BBC/ITN, The BBC/ITN Guide to the New Parliamentary Constituencies, Parliamentary Research Services, 1983.
24. www.electoralcalculus.co.uk and www.ukpollingreport.co.uk; see also D. J. Rossiter, R. J. Johnston and C. J. Pattie 'Estimating the Partisan Impact of Redistricting in Britain', British Journal of Political Science, 27, 1997, 319-31.
25. For a detailed description see Rallings and Thrasher, op. cit, 2007.
26. L. Ware, G. Borisyuk, C. Rallings and M. Thrasher, 'A New Algorithm for Estimating Voter Turnout when the Number of Ballot Papers Issued is Unknown', Electoral Studies, 25, 2006, 59-71.
27. The notional partisan impact of the redistribution undertaken by the Boundary Commission for Northern Ireland is not included in any of the analyses which follow.