There is speculation about how well various new and small parties will do in today’s elections to the Scottish and Welsh Parliaments. Former SNP First-Minister Alex Salmond has recently established the Alba Party, while George Galloway has created Unity 4 All. Both are contesting regional list seats in Scotland. Meanwhile, Abolish the Welsh Assembly has come fourth, with at least 6% of the regional list vote, in all four polls for the Welsh Parliament (Senedd Cymru) since mid-April. Also, Reform-UK, the renamed Brexit Party, is fielding candidates in both countries. These are just some of the various contenders.
This post explains some of the complications in trying to figure out what share of the vote a party needs to get elected in these institutions. It ends up pointing to past experience as a guide and drawing comparison with and the electoral system for the Greater London Assembly (GLA).
TLDR: The experience of all five elections to the Scottish Parliament suggests that around 5.5% of a regional list vote is usually enough to win a seat. It would be rare, but not impossible, to miss out on a seat with 6%. Winning on 5.2% to 5.4% is not uncommon. The lowest D’Hondt ratio ever to yield a seat in Scotland was 4.6% (equivalent to a single party winning a seat on that share). That was in 2003 when the SNP won 5 seats, including 2 list seats, with 23.0% of the Mid Scotland and Fife list vote. For the Senedd, a share of around 6.5% in a region is likely to be enough, especially in North Wales and Mid and West Wales which have historically been more accessible to small parties. By comparison, the GLA has a 5% legal threshold, without which parties would get seats with 3.8% of the vote.
The Scottish Parliament has 129 seats. The electoral system is sometimes described as proportional, but it is significantly different from pure proportional representation. If it were close then a party would win a seat for roughly every 0.8% of the vote, since 100/129=0.8. More precisely, if all the seats were elected by the D’Hondt method of proportional representation a party would be guaranteed a seat with more than 100/(1+Number of seats) per cent of the vote, that is 100/130 = 0.77% of the vote. As we shall see that is much lower than what is actually required to get elected.
Local election seat gains and losses are hideous to try to predict at the best of times. Various factors make this year especially hard. The Covid-19 pandemic means that the 2020 round of local elections was postponed to today, and there have been various boundary changes and restructuring that mean it is hard to allocate many seats to either the 2016-2020 or the 2017-2021 4-year cycle that my model requires. Nonetheless, and despite the weaknesses of my 2019 forecast (discussed below), I have ploughed on regardless. This is not due to the kind of stoic determination that the Finns call sisu: amusingly summarised by someone as, “chin down and press on to the next disappointment.” Rather, I am still curious as to how much of a guide (on a broad macro level) Westminster vote intention polls are to local election outcomes.
Headline forecasts are in the table below together with the range of possible outcomes in the model. The table includes the projections from Michael Thrasher’s second scenario here. He and Colin Rallings would normally calculate an expected National Equivalent Vote (NEV) from the results of local by-elections, but those have not been happening. Instead Michael Thrasher has used adjusted opinion polls to estimate the NEV and then projected the implied changes at the ward/division level. Both mine and his methods use polls this year, but whereas Michael’s is a local projection based on previous ward and division level results, mine is based on regression models of the macro historical relationship between poll changes and net seat changes. (For a really micro, individual-level approach, predicting Labour losses in “red-wall” councils, but not overall net gains and losses, see the analysis from YouGov’s Patrick English here.)
Table 1. Forecasts for English local election net seat changes 2021
-770 to +350
-290 to +430
-50 to +330
It is striking that my forecasts point in different directions from Michael Thrasher’s projections for every party. But with 4630 odd seats up for election, both sets of predictions are for modest net changes. The prediction intervals for my forecasts comfortably include zero for all three parties, so each of them could easily end either up or down when all the results are in.
This post is a revised and updated version of a similar post from 2019 here.
A key summary statistic of the outcome of each year’s annual round of local elections is the so-called Projected National Share (PNS). This is an estimate of the share of the vote that the principal parties would have won in a GB-wide general election if voters across the country as a whole had behaved in the same way as those who actually voted in the local elections. It provides a single, seemingly straightforward measure of party performance that can tell us not only how well or badly a party has done as compared with four years ago (when, typically, most of the seats up for grabs were last contested), but also as compared with any previous local election for which a PNS is available – even though the places in which local elections are held varies considerably from one year to the next.
In this blog we provide some guidance as to how the PNS is being calculated this year by the BBC and how it will be used to project an outcome in terms of House of Commons seats.