APPENDIX - Local and general elections: caveats
There are numerous pitfalls and problems in comparing local and general election voting behaviour. The aim of this part of the analysis has been to draw out the genuine differences in votes cast between the two that are a matter of political choice by the electors. The concurrent nature of the elections in these constituencies means that two factors that normally cloud the comparison (namely the difference in time and context between, say, the London borough elections of 2014 and the general election of 2015, and the fact that turnout is normally around 30-40 per cent in local elections and 60-70 per cent in general elections).
Other comparison problems remain, including:
- Different choices of candidate at local and national level – for instance, UKIP’s coverage in the local elections was incomplete in many areas. Voters who supported UKIP in the general election therefore were unable to mirror this choice in the local elections in many areas (had they wished to) – and therefore voted for other parties, abstained, or spoiled their ballots. In one case, Mid Dorset & North Poole, there were hardly any Labour candidates in the local elections, and the Labour general election vote had to come from somewhere; it is likely that the gap between local and national support for the Lib Dems is not as huge there as it seems from the raw figures.
- A special case of this problem is that some wards had no local elections at all, either because the ward was uncontested (as in Wells), or (as in Colchester) the local election cycle meant that the ward was not up for election in 2015. These cases are compensated for in the results tables(while those with incomplete slates are allowed to stand) using dummy results based on those from 2014 where possible, adjusted for higher turnout and political trends between 2014 and 2015 (i.e. UKIP vote in particular a bit lower, Conservative a bit higher).
- Local elections in many areas – particularly the more rural constituencies – are fought using multi-member wards. Even when the parties all stand candidates for all the vacancies, voters are free to pick and choose between each party’s slate and they often do in considerable numbers. It is therefore not obvious what the party’s baseline vote in the local elections should be. The vote share used here is an average of the two principal methods of calculation – using top candidates’ votes (which exaggerates turnout and the vote share for smaller parties), and using the total votes for all the party’s candidates (which understates the vote share for smaller parties). Both methods distort the number of voters casting ballots, making it impossible to make direct contrasts with the general election numerical vote.
- The franchise is different for local elections. This is a minor factor in most of the seats under discussion here although it is significant in London.