New Seat Details - Trowbridge and West Wiltshire

This page shows the detail of the calculations performed to estimate the general election result for 2017 had the new boundaries for Trowbridge and West Wiltshire 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	33,514	55.8%
LAB	13,720	22.9%
LIB	11,770	19.6%
Green	684	1.1%
OTH	248	0.4%
UKIP	84	0.1%
CON Majority	19,794	33.0%

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.

Trowbridge and West Wiltshire: Map

List of old seats forming part of Trowbridge and West Wiltshire

Old seat: Chippenham

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

Old seat: Chippenham				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
Wiltshire	Bradford-on-Avon North	3,724	Trowbridge and West Wiltshire	1,357	477	958	0	0	0	0	0	2,792
Wiltshire	Bradford-on-Avon South	3,873	Trowbridge and West Wiltshire	1,308	538	957	0	0	0	0	0	2,803
Wiltshire	Chippenham Cepen Park and Derriads	3,326	Chippenham and North Wiltshire	1,668	556	402	0	0	0	0	0	2,626
Wiltshire	Chippenham Cepen Park and Redlands	3,301	Chippenham and North Wiltshire	1,791	677	428	0	0	0	0	0	2,896
Wiltshire	Chippenham Hardenhuish	3,210	Chippenham and North Wiltshire	1,436	574	831	0	0	0	0	0	2,841
Wiltshire	Chippenham Hardens and England	2,987	Chippenham and North Wiltshire	1,206	582	768	0	0	0	0	0	2,556
Wiltshire	Chippenham Lowden and Rowden	3,430	Chippenham and North Wiltshire	1,343	595	829	0	0	0	0	0	2,767
Wiltshire	Chippenham Monkton	2,921	Chippenham and North Wiltshire	1,029	387	800	0	0	0	0	0	2,216
Wiltshire	Chippenham Pewsham	3,266	Chippenham and North Wiltshire	1,283	482	948	0	0	0	0	0	2,713
Wiltshire	Chippenham Queens and Sheldon	3,244	Chippenham and North Wiltshire	1,305	609	768	0	0	0	0	0	2,682
Wiltshire	Corsham Pickwick	3,378	Trowbridge and West Wiltshire	1,647	842	459	0	0	0	0	0	2,948
Wiltshire	Corsham Town	3,712	Trowbridge and West Wiltshire	1,608	438	740	0	0	0	0	0	2,786
Wiltshire	Corsham Without and Box Hill	2,311	Trowbridge and West Wiltshire	1,312	324	268	0	0	0	0	0	1,904
Wiltshire	Hilperton	3,737	Trowbridge and West Wiltshire	1,854	570	474	0	0	0	0	0	2,898
Wiltshire	Holt and Staverton	3,334	Trowbridge and West Wiltshire	1,421	385	873	0	0	0	0	0	2,679
Wiltshire	Melksham Central	3,675	Trowbridge and West Wiltshire	1,480	721	796	0	0	0	0	0	2,997
Wiltshire	Melksham North	3,419	Trowbridge and West Wiltshire	1,402	582	763	0	0	0	0	0	2,747
Wiltshire	Melksham South	3,963	Trowbridge and West Wiltshire	1,415	535	1,032	0	0	0	0	0	2,982
Wiltshire	Melksham Without North	4,093	Trowbridge and West Wiltshire	1,778	436	405	0	0	0	0	0	2,619
Wiltshire	Melksham Without South	3,915	Trowbridge and West Wiltshire	1,954	554	450	0	0	0	0	0	2,958
Wiltshire	Summerham and Seend	784	Trowbridge and West Wiltshire	422	66	70	0	0	0	0	0	558
Wiltshire	Winsley and Westwood	2,969	Trowbridge and West Wiltshire	1,246	305	617	0	0	0	0	0	2,168
	Total	72,572		31,265	11,235	14,636	0	0	0	0	0	57,136

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

Old seat: Devizes

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

Old seat: Devizes				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
Wiltshire	Aldbourne and Ramsbury	3,881	Devizes and East Wiltshire	1,905	448	197	73	90	0	0	16	2,729
Wiltshire	Bromham, Rowde and Potterne	3,784	Devizes and East Wiltshire	1,575	487	183	208	81	0	0	4	2,538
Wiltshire	Bulford, Allington and Figheldean	3,118	Salisbury	1,810	421	184	74	74	0	0	17	2,580
Wiltshire	Burbage and the Bedwyns	3,719	Devizes and East Wiltshire	1,743	486	160	59	75	0	0	5	2,528
Wiltshire	Devizes and Roundway South	3,392	Devizes and East Wiltshire	1,219	608	262	73	87	0	0	19	2,268
Wiltshire	Devizes East	3,003	Devizes and East Wiltshire	1,069	720	183	70	74	0	0	14	2,130
Wiltshire	Devizes North	3,028	Devizes and East Wiltshire	1,021	747	194	69	80	0	0	20	2,131
Wiltshire	Durrington and Larkhill	4,711	Salisbury	2,098	683	839	116	109	0	0	6	3,851
Wiltshire	Ludgershall and Perham Down	3,350	Devizes and East Wiltshire	2,081	582	209	90	88	0	0	13	3,063
Wiltshire	Marlborough East	3,170	Devizes and East Wiltshire	1,099	505	345	67	81	0	0	15	2,112
Wiltshire	Marlborough West	2,848	Devizes and East Wiltshire	1,435	432	218	69	94	0	0	17	2,265
Wiltshire	Pewsey	3,743	Devizes and East Wiltshire	1,457	641	174	63	76	0	0	10	2,421
Wiltshire	Pewsey Vale	3,451	Devizes and East Wiltshire	1,446	408	353	57	66	0	0	3	2,333
Wiltshire	Roundway	3,288	Devizes and East Wiltshire	1,504	530	192	68	79	0	0	13	2,386
Wiltshire	Summerham and Seend	1,152	Trowbridge and West Wiltshire	525	121	51	57	23	0	0	2	779
Wiltshire	The Collingbournes and Netheravon	3,156	Devizes and East Wiltshire	1,570	336	139	55	64	0	0	5	2,169
Wiltshire	The Lavingtons and Erlestoke	3,961	Devizes and East Wiltshire	1,929	725	215	81	97	0	0	5	3,052
Wiltshire	Tidworth	3,759	Devizes and East Wiltshire	3,443	739	313	131	129	0	0	33	4,788
Wiltshire	Urchfont and The Cannings	3,670	Devizes and East Wiltshire	1,312	513	153	177	71	0	0	5	2,231
Wiltshire	West Selkley	3,224	Devizes and East Wiltshire	1,503	478	141	51	68	0	0	3	2,244
	Total	67,408		31,744	10,610	4,705	1,708	1,606	0	0	225	50,598

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

Old seat: Wiltshire North

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

Old seat: Wiltshire North				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
Wiltshire	Box and Colerne	3,670	Chippenham and North Wiltshire	1,776	503	749	28	66	0	0	45	3,167
Wiltshire	Brinkworth	3,687	Chippenham and North Wiltshire	1,884	392	317	44	55	0	0	21	2,713
Wiltshire	By Brook	3,475	Chippenham and North Wiltshire	1,960	368	306	42	52	0	0	10	2,738
Wiltshire	Calne Central	3,164	Devizes and East Wiltshire	1,156	578	659	58	63	0	0	17	2,531
Wiltshire	Calne Chilvester and Abberd	3,770	Devizes and East Wiltshire	1,623	727	575	65	76	0	0	14	3,080
Wiltshire	Calne North	3,095	Devizes and East Wiltshire	1,328	647	780	60	68	0	0	23	2,906
Wiltshire	Calne Rural	3,398	Devizes and East Wiltshire	1,831	397	273	51	54	0	0	45	2,651
Wiltshire	Calne South and Cherhill	3,689	Devizes and East Wiltshire	1,653	491	566	56	67	0	0	26	2,859
Wiltshire	Chippenham Cepen Park and Redlands	54	Chippenham and North Wiltshire	27	13	6	1	1	0	0	0	48
Wiltshire	Chippenham Hardens and England	18	Chippenham and North Wiltshire	7	4	4	0	0	0	0	0	15
Wiltshire	Corsham Pickwick	183	Trowbridge and West Wiltshire	82	52	23	3	4	0	0	1	165
Wiltshire	Corsham Without and Box Hill	1,622	Trowbridge and West Wiltshire	868	278	168	24	31	0	0	6	1,375
Wiltshire	Cricklade and Latton	3,816	Chippenham and North Wiltshire	1,654	500	762	27	66	0	0	14	3,023
Wiltshire	Kington	3,822	Chippenham and North Wiltshire	2,081	423	363	48	61	0	0	13	2,989
Wiltshire	Lyneham	2,876	Chippenham and North Wiltshire	2,273	535	380	59	57	0	0	14	3,318
Wiltshire	Malmesbury	3,790	Chippenham and North Wiltshire	1,592	650	877	59	80	0	0	24	3,282
Wiltshire	Minety	3,700	Chippenham and North Wiltshire	1,996	437	316	51	58	0	0	20	2,878
Wiltshire	Purton	3,637	Chippenham and North Wiltshire	1,848	361	272	25	42	0	0	37	2,585
Wiltshire	Royal Wootton Bassett East	3,654	Chippenham and North Wiltshire	1,768	416	408	25	51	0	0	11	2,679
Wiltshire	Royal Wootton Bassett North	3,395	Chippenham and North Wiltshire	1,410	589	563	59	63	0	0	12	2,696
Wiltshire	Royal Wootton Bassett South	4,612	Chippenham and North Wiltshire	1,538	604	826	66	74	0	0	14	3,122
Wiltshire	Sherston	3,891	Chippenham and North Wiltshire	2,043	433	328	21	50	0	0	10	2,885
	Total	67,018		32,398	9,398	9,521	872	1,139	0	0	377	53,705

The full details of these calculations are given on the Wiltshire North seat details page. Click on "Show workings".

Old seat: Wiltshire South West

The table shows the transfer-adjusted results for each ward in the old seat of Wiltshire South West, as well as showing which new seat each ward is in.

Old seat: Wiltshire South West				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
Wiltshire	Ethandune	3,540	Warminster and Shaftesbury	1,546	602	302	0	67	0	0	13	2,530
Wiltshire	Fovant and Chalke Valley	1,398	Salisbury	804	168	44	0	20	0	0	6	1,042
Wiltshire	Mere	3,319	Warminster and Shaftesbury	1,530	612	138	0	66	0	0	59	2,405
Wiltshire	Nadder and East Knoyle	3,198	Warminster and Shaftesbury	1,675	461	104	0	49	0	0	23	2,312
Wiltshire	Southwick	3,376	Trowbridge and West Wiltshire	1,605	627	160	0	64	0	0	43	2,499
Wiltshire	Summerham and Seend	1,480	Trowbridge and West Wiltshire	760	188	50	0	21	0	0	6	1,025
Wiltshire	Tisbury	3,370	Warminster and Shaftesbury	1,733	513	135	0	59	0	0	11	2,451
Wiltshire	Trowbridge Adcroft	3,128	Trowbridge and West Wiltshire	1,166	816	464	0	77	0	0	15	2,538
Wiltshire	Trowbridge Central	3,254	Trowbridge and West Wiltshire	1,383	1,080	557	0	97	0	0	17	3,134
Wiltshire	Trowbridge Drynham	2,967	Trowbridge and West Wiltshire	1,305	619	279	0	63	0	0	11	2,277
Wiltshire	Trowbridge Grove	3,188	Trowbridge and West Wiltshire	1,384	769	179	0	71	0	0	51	2,454
Wiltshire	Trowbridge Lambrok	3,504	Trowbridge and West Wiltshire	1,530	885	193	0	78	0	0	46	2,732
Wiltshire	Trowbridge Park	3,294	Trowbridge and West Wiltshire	1,328	865	330	0	84	0	0	37	2,644
Wiltshire	Trowbridge Paxcroft	3,715	Trowbridge and West Wiltshire	1,254	601	421	0	65	0	0	12	2,353
Wiltshire	Warminster Broadway	3,465	Warminster and Shaftesbury	1,705	622	170	0	63	0	0	17	2,577
Wiltshire	Warminster Copheap and Wylye	3,404	Warminster and Shaftesbury	2,147	527	137	0	53	0	0	12	2,876
Wiltshire	Warminster East	4,016	Warminster and Shaftesbury	1,797	846	213	0	84	0	0	50	2,990
Wiltshire	Warminster West	3,917	Warminster and Shaftesbury	1,991	672	185	0	66	0	0	15	2,929
Wiltshire	Warminster Without	3,327	Warminster and Shaftesbury	1,774	398	102	0	48	0	0	10	2,332
Wiltshire	Westbury East	3,576	Warminster and Shaftesbury	1,377	787	486	0	85	0	0	53	2,788
Wiltshire	Westbury North	3,228	Warminster and Shaftesbury	1,232	761	438	0	76	0	0	37	2,544
Wiltshire	Westbury West	3,627	Warminster and Shaftesbury	1,695	1,050	239	0	82	0	0	48	3,114
Wiltshire	Winsley and Westwood	292	Trowbridge and West Wiltshire	120	46	33	0	6	0	0	1	206
	Total	71,583		32,841	14,515	5,359	0	1,444	0	0	593	54,752

The full details of these calculations are given on the Wiltshire South West seat details page. Click on "Show workings".

New seat: Trowbridge and West Wiltshire

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: Trowbridge and West Wiltshire
Wiltshire	Bradford-on-Avon North	3,735	Chippenham	1,357	477	958	0	0	0	0	0	2,792
Wiltshire	Bradford-on-Avon South	3,750	Chippenham	1,308	538	957	0	0	0	0	0	2,803
Wiltshire	Corsham Pickwick	3,943	Chippenham	1,647	842	459	0	0	0	0	0	2,948
Wiltshire	Corsham Pickwick	219	Wiltshire North	82	52	23	3	4	0	0	1	165
Wiltshire	Corsham Town	3,727	Chippenham	1,608	438	740	0	0	0	0	0	2,786
Wiltshire	Corsham Without and Box Hill	2,548	Chippenham	1,312	324	268	0	0	0	0	0	1,904
Wiltshire	Corsham Without and Box Hill	1,828	Wiltshire North	868	278	168	24	31	0	0	6	1,375
Wiltshire	Hilperton	3,877	Chippenham	1,854	570	474	0	0	0	0	0	2,898
Wiltshire	Holt and Staverton	3,585	Chippenham	1,421	385	873	0	0	0	0	0	2,679
Wiltshire	Melksham Central	4,010	Chippenham	1,480	721	796	0	0	0	0	0	2,997
Wiltshire	Melksham North	3,675	Chippenham	1,402	582	763	0	0	0	0	0	2,747
Wiltshire	Melksham South	3,989	Chippenham	1,415	535	1,032	0	0	0	0	0	2,982
Wiltshire	Melksham Without North	3,505	Chippenham	1,778	436	405	0	0	0	0	0	2,619
Wiltshire	Melksham Without South	3,956	Chippenham	1,954	554	450	0	0	0	0	0	2,958
Wiltshire	Southwick	3,508	Wiltshire South West	1,605	627	160	0	64	0	0	43	2,499
Wiltshire	Summerham and Seend	747	Chippenham	422	66	70	0	0	0	0	0	558
Wiltshire	Summerham and Seend	1,111	Devizes	525	121	51	57	23	0	0	2	779
Wiltshire	Summerham and Seend	1,440	Wiltshire South West	760	188	50	0	21	0	0	6	1,025
Wiltshire	Trowbridge Adcroft	3,564	Wiltshire South West	1,166	816	464	0	77	0	0	15	2,538
Wiltshire	Trowbridge Central	4,404	Wiltshire South West	1,383	1,080	557	0	97	0	0	17	3,134
Wiltshire	Trowbridge Drynham	3,199	Wiltshire South West	1,305	619	279	0	63	0	0	11	2,277
Wiltshire	Trowbridge Grove	3,445	Wiltshire South West	1,384	769	179	0	71	0	0	51	2,454
Wiltshire	Trowbridge Lambrok	3,838	Wiltshire South West	1,530	885	193	0	78	0	0	46	2,732
Wiltshire	Trowbridge Park	3,714	Wiltshire South West	1,328	865	330	0	84	0	0	37	2,644
Wiltshire	Trowbridge Paxcroft	3,304	Wiltshire South West	1,254	601	421	0	65	0	0	12	2,353
Wiltshire	Winsley and Westwood	2,899	Chippenham	1,246	305	617	0	0	0	0	0	2,168
Wiltshire	Winsley and Westwood	292	Wiltshire South West	120	46	33	0	6	0	0	1	206
	Total	81,812		33,514	13,720	11,770	84	684	0	0	248	60,020

And these are the implied results for 2017 for the new seat of Trowbridge and West Wiltshire. 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:	Michelle Donelan (CON)
County/Area:	Wiltshire (South West)
Electorate:	81,812
Turnout:	73.4%

Trowbridge and West Wiltshire: New Boundaries 2018 Calculation

Trowbridge and West Wiltshire: Overview

Introduction