New Seat Details - Southampton Test

This page shows the detail of the calculations performed to estimate the general election result for 2017 had the new boundaries for Southampton Test 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
LAB	27,432	49.5%
CON	21,883	39.5%
LIB	4,144	7.5%
OTH	722	1.3%
MIN	692	1.2%
Green	493	0.9%
LAB Majority	5,549	10.0%

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.

Southampton Test: Map

List of old seats forming part of Southampton Test

Old seat: Romsey and Southampton North

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

Old seat: Romsey and Southampton 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
Southampton	Bassett	8,890	Southampton Test	4,351	2,200	1,318	0	247	0	0	40	8,156
Southampton	Swaythling	7,385	Southampton Test	3,212	3,022	1,182	0	246	0	0	105	7,767
Test Valley	Abbey	3,786	Test Valley	1,469	408	667	0	73	0	0	13	2,630
Test Valley	Ampfield and Braishfield	1,803	Test Valley	883	141	208	0	13	0	0	7	1,252
Test Valley	Blackwater	4,103	New Forest East	2,062	306	434	0	66	0	0	5	2,873
Test Valley	Broughton and Stockbridge	3,582	Test Valley	1,865	278	396	0	24	0	0	28	2,591
Test Valley	Chilworth, Nursling and Rownhams	5,160	Test Valley	2,493	436	647	0	37	0	0	7	3,620
Test Valley	Cupernham	3,895	Test Valley	1,474	417	872	0	33	0	0	7	2,803
Test Valley	Dun Valley	1,733	New Forest East	895	140	270	0	12	0	0	4	1,321
Test Valley	Harewood	1,748	Test Valley	988	124	142	0	10	0	0	6	1,270
Test Valley	Kings Somborne and Michelmersh	2,106	Test Valley	1,046	160	259	0	13	0	0	3	1,481
Test Valley	North Baddesley	5,382	Test Valley	2,014	563	1,269	0	40	0	0	10	3,896
Test Valley	Over Wallop	1,369	Test Valley	948	125	139	0	8	0	0	2	1,222
Test Valley	Romsey Extra	3,395	Test Valley	1,174	279	416	0	52	0	0	19	1,940
Test Valley	Tadburn	3,989	Test Valley	1,446	435	1,034	0	38	0	0	7	2,960
Test Valley	Valley Park	5,575	Test Valley	2,345	580	1,410	0	42	0	0	8	4,385
	Total	63,901		28,665	9,614	10,663	0	954	0	0	271	50,167

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

Old seat: Southampton Test

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

Old seat: Southampton Test				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
Southampton	Bevois	8,343	Southampton Itchen	1,685	5,299	248	0	0	0	124	103	7,459
Southampton	Coxford	9,843	Southampton Test	1,904	3,639	229	0	0	0	242	202	6,216
Southampton	Freemantle	8,673	Southampton Test	2,780	3,815	296	0	0	0	85	71	7,047
Southampton	Millbrook	9,954	Southampton Test	2,549	3,829	257	0	0	0	92	76	6,803
Southampton	Portswood	8,877	Southampton Test	2,492	3,496	380	0	0	0	109	91	6,568
Southampton	Redbridge	9,871	Southampton Test	2,128	3,946	190	0	0	0	86	72	6,422
Southampton	Shirley	9,212	Southampton Test	2,467	3,485	292	0	0	0	78	65	6,387
	Total	64,773		16,005	27,509	1,892	0	0	0	816	680	46,902

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

New seat: Southampton Test

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: Southampton Test
Southampton	Bassett	10,922	Romsey and Southampton North	4,351	2,200	1,318	0	247	0	0	40	8,156
Southampton	Coxford	9,304	Southampton Test	1,904	3,639	229	0	0	0	242	202	6,216
Southampton	Freemantle	10,548	Southampton Test	2,780	3,815	296	0	0	0	85	71	7,047
Southampton	Millbrook	10,181	Southampton Test	2,549	3,829	257	0	0	0	92	76	6,803
Southampton	Portswood	9,831	Southampton Test	2,492	3,496	380	0	0	0	109	91	6,568
Southampton	Redbridge	9,610	Southampton Test	2,128	3,946	190	0	0	0	86	72	6,422
Southampton	Shirley	9,558	Southampton Test	2,467	3,485	292	0	0	0	78	65	6,387
Southampton	Swaythling	10,402	Romsey and Southampton North	3,212	3,022	1,182	0	246	0	0	105	7,767
	Total	80,356		21,883	27,432	4,144	0	493	0	692	722	55,366

And these are the implied results for 2017 for the new seat of Southampton Test. 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:	Alan Whitehead (LAB)
County/Area:	Hampshire (South East)
Electorate:	80,356
Turnout:	68.9%

Southampton Test: New Boundaries 2018 Calculation

Southampton Test: Overview

Introduction