Smith, Timothy Edward Hallam
(2019)
Incumbency advantage of UK members of Parliament 1959 -2010.
PhD thesis, University of Nottingham.
Abstract
This thesis provides original quantitative research on MPs’ incumbency advantage in Great Britain from 1959 – 2010. It has been widely agreed since the 1970s that MPs benefit from a small but significant personal vote, such that when they retire, their party receives a penalty in their constituency as a newcomer fights the seat. Much of the empirical work done on incumbency, discussed in the literature review, has been done using individual level data, i.e. asking voters questions about who they vote for and why they do so. This study is based entirely on macro-level data, that of election results. The author felt that whilst voters could provide ex-post facto rationalization or even lies to survey takers about their reasons for voting, election vote counts do not lie. The study adapts two methods of measuring incumbency popular in the US, "slurge" and the "Gelman King Index” for work on Congress, for use in the UK setting.
The thesis is structured with Chapter 1 providing some real life examples of incumbency advantage looking through MPs careers. As well as providing some original qualitative research on incumbency, it also explains some of the challenges and pitfalls of using macro level data to measure incumbency advantage. The literature review is divided into two chapters. Chapter 2 looks at the history of research into incumbency advantage and explores how methodologies have changed. Chapter 3 looks thematically through the differing sources from which academics believe incumbency advantage comes. Chapter 4 presents some original quantitative research on the change in the operation of the UK electoral system over the study period. Chapter 5 presents the methods and data, Chapter 6 the results and Chapter 7 the conclusions and implications.
The key findings of the thesis are:
• Incumbency advantage is significant and positive for the Conservatives, Labour, Liberal Democrats and the two nationalist parties in Wales and Scotland and has been so for the whole of the study period
• There is a considerable difference amongst the parties, in the 1983 – 2010 period, Conservative incumbency advantage was worth just under 1% of the vote, Labour’s was 2% of the vote, whilst the Liberals and Nationalists enjoyed an incumbency advantage of 4 – 8% of the vote
• There has been an increase over time in incumbency advantage over the study with major party incumbency advantage increasing from under 0.5% of the vote in the early period to 1.5-2.5% in the most recent elections.
• There is tentative evidence that incumbency advantage is larger for the major parties in areas where they have fewer MPs.
• That incumbency advantage has been important enough to change the results of as many as 10 to 15 seats in recent elections. Without incumbency effects, the Conservatives would have been likely to have won an extra 13 seats at the 2010 election, giving them a realistic option to govern as a minority if they had not wanted to come to an agreement with the Liberal Democrats.
• The study finds no material evidence that the decline in partisanship amongst voters is responsible for the increase in incumbency advantage.
• Whilst many US authors believe that House incumbency advantage is inversely correlated with the polarization of the two parties, the study found no evidence of this in the UK setting.
• Tests on controversial roll-call votes such as the Iraq War show no evidence that it makes a material difference to an MP’s electoral performance in a subsequent election. The results suggest that the electorate does not know or care (enough) about how their MP voted even in the most critical divisions for it to make a difference to whether they vote for them or not.
• Whilst the thesis does not come to a firm conclusion about the source of incumbency advantage, it finds strong circumstantial evidence that the main source is name recognition. This comes from the results of tests on non-incumbent repeat candidates. Amongst Conservatives, there was no significant difference between incumbency advantage and the bonus received by non-incumbent repeat candidates.
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