New Seat Details - Carshalton and Wallington

This page shows the detail of the calculations performed to estimate the general election result for 2017 had the new boundaries for Carshalton and Wallington been in force at that time. The basic idea of the calculation is to look at the district council wards which make up the new seat, and estimate how they voted in 2017. This estimate is based on the recent local election results in those wards, with adjustments made to allow for different turnouts and different voting patterns for local and general elections.

In many cases, wards are divided between several old constituencies or between new constituencies. So the same ward may be shown more than once, but the electorate shown will reflect that ward sub-section.

Election results from a recent local election are given. This is usually the local election closest to 2015 from the period 2012-2015. For multiple-member wards, the votes shown are the sum of the votes cast for all candidates of each party. A negative number indicates candidate(s) elected unopposed.

Calculation method

There are two problems with using the raw (actual) local election results to imply general election results ward-by-ward. Firstly, turnout can be different between local and general elections, which means that the total number of local votes cast does not equal the number of votes cast in each old seat at the general election. To correct for this, we adjust the local votes to match the general election turnout. Each ward's result is scaled, whilst keeping constant the percentage support for each party, so that the total turnout adds up to the old seat's general election turnout. All wards in the old seat are assumed to have the same percentage turnout.

Party	Implied 2017 Votes	Implied 2017 Share
CON	22,849	40.6%
LIB	21,813	38.8%
LAB	10,413	18.5%
Green	576	1.0%
MIN	434	0.8%
OTH	188	0.3%
CON Majority	1,036	1.8%

Secondly, even though we now have the correct number of votes in the old seat, the party totals will not match the general election result. Some parties do better at the local election than the general election, and others do vice versa. We call these strong and weak parties respectively. The next step is to transfer votes from strong parties to weak parties. This is done by taking votes proportionally away from strong parties and putting them in a transfer pool. For instance if a party got 12,500 local votes, but only 10,000 general election votes, it will lose 20% over all the wards. These votes in each ward will be put in the ward's transfer pool and allocated to the weak parties. Weak parties will get votes transferred to them in proportion to the votes they need over the old seat. For instance, if two weak parties need 4,000 and 1,000 votes respectively, the first party will get 80% of each ward's transfer pool and the second party will get 20% of each ward's transfer pool. The transfer of votes between parties is done using the Electoral Calculus Transition Model.

Carshalton and Wallington: Map

List of old seats forming part of Carshalton and Wallington

Old seat: Carshalton and Wallington

The table shows the transfer-adjusted results for each ward in the old seat of Carshalton and Wallington, as well as showing which new seat each ward is in.

Old seat: Carshalton and Wallington				Transfer-adjusted Results
District	Ward	Electorate 2017	New Seat	CON Votes	LAB Votes	LIB Votes	UKIP Votes	Green Votes	NAT Votes	MIN Votes	OTH Votes	Total Votes
Sutton	Beddington North	7,636	Carshalton and Wallington	2,133	1,029	2,231	0	60	0	31	14	5,498
Sutton	Beddington South	7,734	Carshalton and Wallington	2,485	1,002	2,079	0	24	0	56	24	5,670
Sutton	Carshalton Central	7,529	Carshalton and Wallington	2,238	701	2,304	0	68	0	49	22	5,382
Sutton	Carshalton South and Clockhouse	7,523	Carshalton and Wallington	2,615	540	1,904	0	53	0	42	18	5,172
Sutton	St Helier	7,544	Carshalton and Wallington	1,837	1,814	2,623	0	31	0	42	18	6,365
Sutton	The Wrythe	7,439	Carshalton and Wallington	1,809	938	2,454	0	60	0	37	16	5,314
Sutton	Wallington North	7,749	Carshalton and Wallington	2,322	890	2,342	0	73	0	36	16	5,679
Sutton	Wallington South	7,496	Carshalton and Wallington	2,076	752	2,415	0	66	0	107	46	5,462
Sutton	Wandle Valley	7,654	Carshalton and Wallington	1,934	1,694	2,465	0	66	0	34	14	6,207
	Total	68,304		19,449	9,360	20,817	0	501	0	434	188	50,749

The full details of these calculations are given on the Carshalton and Wallington seat details page. Click on "Show workings".

Old seat: Sutton and Cheam

The table shows the transfer-adjusted results for each ward in the old seat of Sutton and Cheam, as well as showing which new seat each ward is in.

Old seat: Sutton and Cheam				Transfer-adjusted Results
District	Ward	Electorate 2017	New Seat	CON Votes	LAB Votes	LIB Votes	UKIP Votes	Green Votes	NAT Votes	MIN Votes	OTH Votes	Total Votes
Sutton	Belmont	7,275	Carshalton and Wallington	3,400	1,053	996	0	75	0	0	0	5,524
Sutton	Cheam	7,852	Sutton and Cheam	3,469	786	1,371	0	61	0	0	0	5,687
Sutton	Nonsuch	7,922	Sutton and Cheam	3,211	999	1,597	0	63	0	0	0	5,870
Sutton	Stonecot	8,007	Sutton and Cheam	2,882	1,221	1,614	0	155	0	0	0	5,872
Sutton	Sutton Central	7,145	Sutton and Cheam	2,433	1,695	1,718	0	203	0	0	0	6,049
Sutton	Sutton North	7,189	Sutton and Cheam	2,530	1,280	1,730	0	71	0	0	0	5,611
Sutton	Sutton South	6,664	Sutton and Cheam	2,729	1,030	1,395	0	81	0	0	0	5,235
Sutton	Sutton West	7,322	Sutton and Cheam	2,648	1,252	1,788	0	84	0	0	0	5,772
Sutton	Worcester Park	8,324	Sutton and Cheam	3,266	1,348	1,661	0	79	0	0	0	6,354
	Total	67,700		26,568	10,664	13,870	0	872	0	0	0	51,974

The full details of these calculations are given on the Sutton and Cheam seat details page. Click on "Show workings".

New seat: Carshalton and Wallington

District	Ward	Electorate 2017	Old Seat	CON Votes	LAB Votes	LIB Votes	UKIP Votes	Green Votes	NAT Votes	MIN Votes	OTH Votes	Total Votes
New seat: Carshalton and Wallington
Sutton	Beddington North	7,675	Carshalton and Wallington	2,133	1,029	2,231	0	60	0	31	14	5,498
Sutton	Beddington South	7,915	Carshalton and Wallington	2,485	1,002	2,079	0	24	0	56	24	5,670
Sutton	Belmont	7,483	Sutton and Cheam	3,400	1,053	996	0	75	0	0	0	5,524
Sutton	Carshalton Central	7,514	Carshalton and Wallington	2,238	701	2,304	0	68	0	49	22	5,382
Sutton	Carshalton South and Clockhouse	7,221	Carshalton and Wallington	2,615	540	1,904	0	53	0	42	18	5,172
Sutton	St Helier	8,885	Carshalton and Wallington	1,837	1,814	2,623	0	31	0	42	18	6,365
Sutton	The Wrythe	7,420	Carshalton and Wallington	1,809	938	2,454	0	60	0	37	16	5,314
Sutton	Wallington North	7,928	Carshalton and Wallington	2,322	890	2,342	0	73	0	36	16	5,679
Sutton	Wallington South	7,625	Carshalton and Wallington	2,076	752	2,415	0	66	0	107	46	5,462
Sutton	Wandle Valley	8,665	Carshalton and Wallington	1,934	1,694	2,465	0	66	0	34	14	6,207
	Total	78,331		22,849	10,413	21,813	0	576	0	434	188	56,273

And these are the implied results for 2017 for the new seat of Carshalton and Wallington. Please note that the wards used are those of 2015 in order to be consistent with those used by the Boundary Commissions.

Implied MP at 2017:	Unknown (changed seat) (CON)
County/Area:	Sutton (London)
Electorate:	78,331
Turnout:	71.8%

Carshalton and Wallington: New Boundaries 2018 Calculation

Carshalton and Wallington: Overview

Introduction