Fifth combined forecast for the 2024 general election

By Stephen Fisher, John Kenny, Paul Furey, and Polina Ryzhuk. 26^th June 2024.

The average of different kinds of seats forecasts points to a Labour majority of 200; the same as last week. There is very little change for other parties, except that the average forecast for the Conservatives is down from 127 last week to 123 this week. That is despite a rise for the Tories in the simple-model projections (uniform change from opinion polls). The Conservative seat forecast is down in both the non-MRP complex models and the MRP average, which is now forecasting just 92 seats for the Conservatives. That average is now based on 9 different MRP models.

Table 1. Seat Forecasts

	Betting Markets	Complex models	Simple models	MRP	Average
Con	89	119	194	92	123
Lab	434	431	381	453	425
LD	52	54	36	55	49
Reform	4	4	0	4	3
Green	2	1	1	2	2
SNP	21	20	17	21	20
PC	3	3	3	3	3
Lab majority	218	212	112	256	200

Table 2 below lists the latest MRP estimates. The variance between them continues to be remarkable.

Table 2. MRP seat forecasts

	Lab	Con	LD	Reform	Greens	SNP	PC	Majority
Electoral Calculus	457	76	66	3	2	22	4	264
Find Out Now	450	60	71	18	4	24	4	250
Focaldata	450	110	50	1	1	16	2	250
Ipsos	453	115	38	3	3	15	4	256
More in Common	406	155	49	0	1	18	2	162
Savanta	516	53	50	0	0	8	4	382
Survation	456	72	56	7	1	37	2	262
We Think	465	76	52	3	3	29	3	280
YouGov	425	108	67	5	2	20	4	200
Average	453	92	55	4	2	21	3	255

Figure 1 shows how the forecasts of the size of a Labour majority have changed since the start of the campaign.

Figure 1. Forecasts for the size of a Labour majority

Table 3 shows estimates of probabilities and pseudo probabilities for different election outcomes. Averaging the different sources suggests a 95% chance of a Labour government and an 90% chance of a Labour majority. Both numbers one point higher than the corresponding estimates from last week.

Table 3. Probabilities (%)

	Betting markets	Models	Polls	Citizen forecast	Volunteered	Average
Lab Majority	97	96	100	67		90
Lab 100+ Majority			61			61
Con led Gov	3		0	17	0	5
Lab led Gov	98		100	83	100	95

Figure 2 shows how stable the predicted probabilities of a Labour majority have been since the start of the campaign.

Figure 2. Predicted probabilities of a Labour majority

Table 4 summarises forecasts for vote shares. The Conservatives and Labour are down a point each again this week. The Labour lead remains at 20 points. Reform UK, are up a further point, to 16 per cent. No net change since last week for the Liberal Democrats and the Greens.

Table 4. Vote share forecasts (%GB except where stated)

	Poll aggregates	Betting markets	Models	MRP	Average
Con	21	21	20	23	21
Lab	41	40	41	42	41
Lib Dem	11	11	11	11	11
Reform	16	17	17	13	16
Green	6		6	5	6
SNP (Scotland)	31		32		31
PC (Wales only)	14		12		13
Lab-Con lead	20	19	21	19	20

Figure 3 shows the forecasts for the Labour lead over the Conservatives in the GB share of the vote. The betting markets have converged with the average MRP estimate of the lead. But all the indicators remain very similar and the lead has been very stable.

Figure 3. Forecasts for the Labour lead in vote share

Estimates come from data collected late afternoon and early evening on 26^th June 2024.

Methodology

The idea of combining forecasts from different sources has a good track record, though it has to be admitted that our attempts for the 2017 general election and the 2016 Brexit referendum did not work out so well. For reviews of previous combined forecasts here for 2017 and here for 2019. Also worth noting is the experience of the pollyvote.com combined forecast of the US presidential elections.

The basic approach is to combine forecasts by averaging them within each category and then average across categories. Since the different sources do not all present similar figures that can be averaged on a like-for-like basis there are various judgement calls we have had to make on how to treat the data.

Polls

For vote shares, we use the various available polling averages. Some admittedly are quite sophisticated, allowing for house effects, but they are nonetheless estimates of current public opinion and not future votes.

To estimate a pseudo-probability of a Labour majority from the polls, we take the proportion of pollsters with a GB Labour lead greater than 12 points, on the basis that this is the level required for a Labour majority under traditional uniform change assumptions. Similarly, the proportion of the most recent polls from each pollster with a lead of 19 points or more serves as a pseudo probability for the chances of a Labour majority of over 100 (making allowances for current polling in Scotland and Wales).

Statistical models

We have divided statistical models into simple (poll average plus uniform swing seats projections), Multilevel Regression and Poststratification (MRP), and other complex models (anything more elaborate than uniform change but not necessarily particularly complex). Within these categories we simply average the available estimates of seats and shares. We have not excluded any models based on quality, but they do have to be statistical models as opposed to personal guesses.

Betting markets

For the seats forecasts we are using the mid points of the spread betting for the markets. The markets might collectively imply fewer or more seats forecast for the parties in total than there are seats to be won in Britain. This is because the markets are separate for each party and do not need to be consistent collectively.

Betting markets for shares of the vote are typically done in bands. We take the mid points of the bands with the highest implied probabilities weighted by their implied probabilities from the betting odds. We then average across bookies.

Citizen forecasts

Some polls ask people what they think that the outcome of the election will be. We call these ‘citizen forecasts.’ Different pollsters use different survey questions but they can be combined to generate pseudo-probabilities. We use the proportion of poll respondents who think there will be a Labour majority, excluding “don’t knows” and re-percentaging, as the pseudo-probability of a Labour majority. We treat the question of whether Rishi Sunak will continue as prime minister to be equivalent to the Conservatives getting a majority, because they do not have any clear governing partners in the event of a hung parliament. Where appropriate, the probability of a Labour led government is taken to be 100 minus the probability of a Conservative led one. But that is not the case for questions where respondents are given the chance to say they think there will be some “other” kind of government. We use the most recent poll with a citizen forecast survey question from each pollster and only those in recent weeks. Only a few pollsters ask citizen forecast questions.

Volunteered forecasts

These come from the Good Judgement Project, which encourages people to forecast the outcomes of various events in order to develop and improve their forecasting skills. The people providing their predictions to the Good Judgement Project are not necessarily experts, but nor can they be seen as a representative sample, and so we report their predictions separately as ‘volunteered’ forecasts.

Sources:

Betting Markets:

Models (Elaborate):

Bradshaw Advisory