By John Curtice and Stephen Fisher.
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.
Continue reading Calculating the Local Elections Projected National Share (PNS) and Projected House of Commons in 2019
By Stephen Fisher.
Updated 23:00 on 1st May to include a poll-based forecast I did not previously have access to, and to clarify figures for the Rallings and Thrasher local by-election model based forecast.
My predictions for this week’s bumper crop of English council elections are given in Table 1 below, along with those of others. The changes are relative to (sometimes notional) results for 2015 when the seats were last fought.
Table 1. Forecasts for English local election net seat changes 2019
||R&T (local by-election model)
||R&T (local vote intention poll)
||-90 to -1,300
||+200 to +990
||-10 to +720
R&T refers to Colin Rallings and Michael Thrasher. Their figures are, I’m told, in the hard copy version of their Sunday Times article. (They differ slightly from those on Sophy Ridge on Sunday and others being attributed to them on Twitter.) Their local by-election model takes the results of recent local by-elections to predict the National Equivalent Vote (NEV) and projects the implied NEV changes since 2015 at the ward level (perhaps using notional results where required.) The local-election vote-intention poll Rallings and Thrasher used was conducted by Opinium which had the following shares of the vote: Con 28, Lab 36, LD 10, UKIP 9. That poll-based forecast is also mentioned in this excellent blog on the background to the local elections, which includes great data visualisation.
Continue reading Forecasting Local Election Net Seat Gains/Losses 2019
By Stephen Fisher.
People often wonder what local election results bode for the next general election. Here is a quick look at the relationship between the BBC Projected National Share of the vote (PNS) in the local elections and the outcome of subsequent general elections. In particular, I focus on the lead for the main opposition party over the principal governing party. The graphs below show the lead at the subsequent general election plotted against the lead in the PNS.
Continue reading How big a lead does Labour need in the local elections to be on course to win the next general election?
By John Curtice and Stephen Fisher.
Part of the ritual of election-night coverage at the BBC is the calculation of 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, but also as compared with any previous local elections for which a PNS is available – even though the places in which local elections are held varies considerably from one year to the next.
One of the key patterns in last year’s general election results was a tendency for those who voted Remain to swing more to Labour than those who voted Leave, while the Conservatives lost ground amongst Remain voters while advancing amongst their Leave counterparts. If a similar pattern is maintained at these local elections – and it was in last year’s county council elections – then the Labour vote will increase more (or fall less) were the Remain vote was higher in 2016, while the converse will be true of the Conservatives.
Continue reading Calculating the local elections Projected National Share (PNS) in 2018
by Stephen Fisher
My forecasting model for seat gains/losses at local elections has previously been a simple model based on change in party support in the polls. While the historical data show that changes in the percentage of the council seats that a party wins is reasonably strongly correlated with changes in that party’s poll share, that basis for forecasting this year would not work.
The Conservatives are up by 8 points and Labour up by 6 points in the polls since just before the 2014 local elections, when most the seats up for election this week were last fought. As in last year’s general election, support for both main parties has increased largely because of a big drop in UKIP support. Forecasting the parties separately based on changes in their respective poll shares would produce misleading predictions of big gains for both main parties. In first-past-the-post elections it is typically relative not absolute performance that matters for seat outcomes. Last year, despite winning more votes the Conservatives lost their parliamentary majority because the Labour vote share went up by more than did that for the Conservatives.
For this reason, my forecasting models this year are based on changes in the gaps between polls shares. For the Conservatives, who have traditionally faced many contests with the Liberal Democrats, their leads over both Labour and the Liberal Democrats matter. For Labour, the model is primarily based on the Labour lead over the Conservatives. Meanwhile, for the Liberal Democrats, their changing opinion poll performance relative to the Conservatives, but not Labour, has historically been correlated with headline local election seat changes.
Continue reading Forecasting Local Election Seat Gains/Losses 2018
By Stephen Fisher.
UKIP are putting up just 377 candidates at the general election, well short of the 624 they had in 2015. Given that the polls are showing that around half of former UKIP voters are planning on voting Conservative this year, and given that the Conservatives clearly benefitted from the collapse of the UKIP vote in the local elections, surely UKIP dropout is a big advantage for Theresa May?
Perhaps not. A good way of assessing this question is to look at the experience of local elections and analyse how much other parties benefitted when UKIP stood a candidate in 2013 but not this year, compared with where they had candidates both times. To make the context more like a general election I focus just on places fought by the Conservatives, Labour and the Liberal Democrats both in 2013 and 2017.
There were 969 such divisions where the BBC collected the full details of the result. Of these 523 had UKIP candidates both times, and 446 had a UKIP candidate last time but not this time – only a slightly higher (46%) dropout rate than that for the general election (40%).
Continue reading UKIP dropout did not help the Conservatives much in the local elections
by Stephen Fisher.
Update 18.40, 4.5.17: I was mistaken as to the method for the Rallings and Thrasher projection, the details have now been corrected. Nothing about my forecast has changed.
This is definitely just for curiosity value only! Last week Roger Scully released the results of his Welsh Political Barometer survey which included Westminster and local election vote intention questions see here. The changes on the comparable survey from just before the last main round of Welsh local elections five years ago are presented in the first and third columns of the table below. Colin Rallings and Michael Thrasher did a seat projection based on the change from the actual 2012/3 local election vote share to the 2017 local-vote intention poll (Con +13, Lab -8, LD -1, PC +3), as discussed by Roger Scully here and listed in the second column of the table.
||Rallings & Thrasher
The final column of the table represents my attempt to translate the changes in the Westminster vote intention into changes in local election seats, similarly to the way I did for the English local elections. Regression analysis of local election results in Wales since 1995 shows strong linear relationships between votes and seats for each of the main parties, with the partial exception of the Liberal Democrats. On average the main parties have picked up around 16 extra seats for every percentage point extra in the overall share of the vote (just 12 for the Lib Dems).
If this relationship were to continue and if the changes in the opinion polls since 2012 were to be reflected in the results then the numbers of gains and losses would be much bigger than suggested in the Rallings and Thrasher projection. For instance Labour would be expected to lose 320 not just 130 seats.
By implication the geography of local election voting must be doing a lot of work to dampen the scale of gains and losses for the Conservatives and Labour parties in the Rallings and Thrasher projection. It would seem that there are a lot very safe Labour council seats in Wales and the system is extremely biased to Labour. The Rallings and Thrasher projection implies that the Labour would win with a 2 point lead over the Conservatives in votes, but more than twice as many seats (450 to 195). That would be extraordinarily unjust.
Projecting the changes in the Westminster vote intention on to seats with the regression method (final two columns) suggests the Conservatives will emerge (for the first time in a long time) with a substantial lead in both votes and seats.
Thanks to Eilidh Macfarlane for help with the data.