APPENDIX 1: THE RESULtS ANaLYSED John Curtice, Stephen Fisher, Robert Ford and Patrick English The outcome of the 2017 election seems to pose a serious challenge to claims about the decline of Britain’s two-party system. No less than 84.5% of the UK-wide vote was cast for either the Conservatives or Labour, well above the proportion at any election since 1970. At 2.88, the effective number of parties in the electorate (as conventionally calculated) is still somewhat above two, but is now well down on the figure of 3.71 that pertained as recently as 2010.1 But the term ‘two-party system’, is often used to imply more than two parties dominating the vote. Amongst other things, it is also taken to refer to a system in which power and ministerial office alternate between the Conservatives and Labour, one of whom, thanks to the electoral system, always enjoys an overall majority in the House of Commons. But in 2017 no single party secured an overall major- ity, and the election resulted in a minority Conservative government backed by a ‘confidence and supply’ arrangement with the DUP. This fol- lows an election in 2010 which also resulted in a hung parliament (and the formation of the country’s first post-war coalition) and another in 2015 that gave the Conservatives a majority of just 12, a majority that in precipi- tating the early 2017 ballot Theresa May indicated was too small. There is another reason to question whether the outcome of the 2017 election necessarily represented a return to some kind of ‘normality’. The ballot took place just 12 months after a deeply disruptive referendum on the UK’s membership of the EU in which many voters failed to follow the advice of their party or party leader as to how they should vote. In seeking © The Author(s) 2018 449 P. Cowley, D. Kavanagh, The British General Election of 2017, https://doi.org/10.1007/978-3-319-95936-8 450 APPENDIX 1: THE RESULTS ANALYSED an enlarged majority, the Prime Minister stated that her purpose was to seek a mandate for her vision of Brexit. If, as a result, voters were inclined to align their vote in the election with their preference in the 2016 refer- endum, the pattern of support for the parties might well have changed substantially and look rather different from what we might once have anticipated. The aim of this appendix is to examine how the pattern of support for the parties changed between 2015 and 2017. We focus in particular on how far the parties’ performances reflect the pattern of voting in the 2016 EU referendum and on the extent to which those performances did or did not represent a departure from the past. We also assess how the way peo- ple voted was reflected and refracted by the electoral system, and why it once again did not provide any party with an overall majority. Our evi- dence is derived from an analysis of the rises and falls in party support since 2015 across the 632 constituencies in Great Britain (for a brief discussion of the outcome in Northern Ireland, where the party system is very differ- ent, see p. 244). MEaSUrING CHaNGE Our principal measure of a party’s performance in a constituency is the change in its share of the vote, that is, the difference between the percent- age of the vote it won this time and the share it won in 2015. We usually calculate this change wherever a party contested the constituency at both elections. The Speaker’s seat (Buckingham) was not contested by either Labour or the Liberal Democrats and is thus excluded from all our analy- ses of change in party support. On this occasion, the Liberal Democrats also did not fight Brighton Pavilion or Skipton & Ripon, so these two seats are also excluded in our analysis of Liberal Democrat performance. Meanwhile, after having fought 614 of the 632 seats in Great Britain in 2015 (including every seat in England and Wales), UKIP only contested 378 constituencies this time. This dramatic reduction requires us on occa- sion to take into account in our analysis the drop in the UKIP vote occa- sioned as a result of the party’s decision not to fight a seat again, as well as the change in the party’s share of the vote in the 376 comparable constitu- encies where the party stood in both 2015 and 2017. The Greens, too, fought rather fewer seats, but in their case the drop was less dramatic, from 568 seats in 2015 to 460 this time. APPENDIX 1: THE RESULTS ANALYSED 451 Table A1.1 summarises the level and distribution (across all constituen- cies in Great Britain) of the change in the share of the vote for those par- ties that fought all or most of the seats in 2015 or 2017. It shows the change in each party’s overall share of the vote across Britain as a whole, together with: (1) the average (mean) change across all of the seats the party contested in 2015 and 2017; and (2) the median change across con- stituencies (that is, the value which divides the constituency changes into two equally sized groups). At this election, these various figures are in most instances very similar to each other. In the case of UKIP, we both summarise what happened in those seats that the party fought both times and across all constituencies, irrespective of the pattern of UKIP candida- ture. The table also shows two measures of the relative performance of the Conservatives and Labour known as ‘swing’. These have often featured prominently in previous appendices in this series, but we will make only occasional reference to either measure in this appendix.2 Whichever measure of change we examine, this was clearly an election at which the fortunes of many parties changed dramatically. According to the Pedersen Index, a summary measure of the extent of the change in party support between two elections, this was the second election in a row Table A1.1 Measures of change since 2015 Overall Mean Median Standard deviation Change in Con vote +5.8 +5.9 +6.0 5.9 Change in Lab vote +9.8 +9.5 +9.8 4.6 Change in Lib Dem vote −0.5 −0.6 −0.5 3.8 Change in UKIP vote −11.8 −12.0 4.6 (seat fought both times) Change in UKIP vote −11.0 −11.1 −11.7 5.3 (regardless of candidature) Change in Green vote −2.2 −2.4 −1.9 2.0 Total vote swing −2.0 −1.8 −2.0 4.4 Two-party swing −3.3 −2.1 −3.9 7.5 Change in turnout +2.4 +2.4 +2.8 3.1 Notes: Buckingham (no Labour or Liberal Democrat candidates in 2015 and 2017) is excluded from the calculation of the mean, median and standard deviation of all statistics apart from turnout. The seat is also excluded from all analysis of party performance in this appendix. Total vote swing is the average of the change in the Conservative share of the vote and the Labour share of the vote. Two-party swing is the change in the Conservative share of the votes cast for Conservative and Labour only (that is, the two-party vote). In both cases a plus sign indicates a swing to the Conservatives, and a minus sign a swing to Labour 452 APPENDIX 1: THE RESULTS ANALYSED that was more volatile than any of the contests between 1945 and 2010.3 The increase in Labour’s share of the vote was the biggest the party had enjoyed since the 1945 election, while the increase in Conservative sup- port was the largest increase in support enjoyed by any incumbent govern- ment that had won the previous election since the 1832 Reform Act. In contrast, thanks primarily to a collapse in UKIP support, the combined level of support for parties other than the Conservatives, Labour and the Liberal Democrats dropped markedly from the all-­time high of 23% that it reached in 2015 to just 8%, the lowest level since 2005. Table A1.1 also shows the standard deviation, a measure of the extent to which the change in a party’s vote share varied from one constituency to another. From this we can see that it was the Conservatives’ perfor- mance that varied most across the country. In previous appendices in this series we have consistently reported that the Conservatives’ performance varied least from one place to another. However, at this election, at 5.9, the standard deviation statistic for the change in the Conservatives’ share of the vote is higher than at any previous post-war contest. Typically, we do not expect, because historically it has not normally been the case, that the change in a party’s share of the vote will be propor- tional to (or in any other way related to) the share of the vote it won at the last election.4 However, there have been some recent noticeable excep- tions. The sharp fall in Labour’s vote in 2010 (and, equally, the dramatic drop in its support in Scotland in 2015) together with the collapse in the Liberal Democrat vote in 2015 were both more limited in those places where the party in question had previously been weaker—because, arith- metically, its support could not fall as heavily in such seats. The sharp drop in the UKIP vote this time creates a similar situation.