Islwyn: New Boundaries Calculation

Due to changes in ward boundaries, some new wards are divided among several old constituencies (though never between two new constituencies). Such wards are shown divided into several parts, called [1], [2], and so on.

Election results from a recent local election are given. This is usually the local election from 2003, 2004 or 2006. 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. Where zero votes are shown, the ward is not needed because the entire old seat is unsplit.

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.

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% of its votes from each ward. 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 on a ward-by-ward basis using these common percentages.

More details of the calculation formulas are available.

The old seat(s) needed are:

• Islwyn
• Caerphilly

Old seat: Islwyn

					Actual Results					Turnout-adjusted Results						Transfer-adjusted Results
District	Ward	Electorate 2005	Old Seat	New Seat	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	Total Votes	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	Total Votes
Caerphilly	Abercarn	3,669	Islwyn	Islwyn	0	1,728	0	875	0	0	1,455	0	737	0	2,192	90	1,650	168	283	0	2,192
Caerphilly	Argoed	1,989	Islwyn	Islwyn	0	457	0	223	0	0	799	0	390	0	1,189	47	902	89	149	0	1,189
Caerphilly	Blackwood	6,373	Islwyn	Islwyn	394	1,984	0	920	2,412	263	1,323	0	613	1,608	3,807	657	2,177	736	235	0	3,807
Caerphilly	Cefn Fforest	2,878	Islwyn	Islwyn	76	973	0	438	838	56	720	0	324	620	1,720	218	1,072	304	124	0	1,720
Caerphilly	Crosskeys	2,560	Islwyn	Islwyn	108	749	0	195	0	157	1,089	0	283	0	1,529	191	1,164	64	108	0	1,529
Caerphilly	Crumlin	4,496	Islwyn	Islwyn	0	1,563	0	2,011	0	0	1,175	0	1,511	0	2,686	184	1,575	345	580	0	2,686
Caerphilly	Newbridge	4,870	Islwyn	Islwyn	424	2,295	0	2,709	0	227	1,230	0	1,452	0	2,909	404	1,614	331	557	0	2,909
Caerphilly	Pengam	2,986	Islwyn	Islwyn	95	1,247	0	628	187	79	1,031	0	519	155	1,784	173	1,235	176	199	0	1,784
Caerphilly	Penmaen	3,687	Islwyn	Islwyn	203	908	0	1,336	523	151	673	0	991	388	2,203	349	1,102	370	380	0	2,203
Caerphilly	Pontllanfraith	6,277	Islwyn	Islwyn	647	2,725	0	2,631	636	365	1,539	0	1,486	359	3,749	618	2,087	472	570	0	3,749
Caerphilly	Risca East	4,804	Islwyn	Islwyn	0	2,539	454	578	0	0	2,040	365	465	0	2,870	56	2,163	471	178	0	2,870
Caerphilly	Risca West	4,160	Islwyn	Islwyn	211	1,921	0	751	0	182	1,656	0	647	0	2,485	261	1,827	147	248	0	2,485
Caerphilly	Ynysddu	2,918	Islwyn	Islwyn	0	1,174	0	1,136	0	0	886	0	857	0	1,743	104	1,113	195	329	0	1,743
	Total		Islwyn							1,480	15,616	365	10,275	3,130	30,866	3,358	19,687	3,873	3,947	0	30,866

The transfer table below shows the votes cast in the old seat of Islwyn at the general election, as well as the total local turnout-adjusted votes. The number of votes to transfer, shown in the fourth and fifth columns, are the difference between the general and local votes. Strong parties will have votes transferred away, and weak parties will have votes transferred into them. The final column describes how votes will be transferred away from or into that party on a ward-by-ward basis. If a party is too strong, it will lose a percentage of its votes in each ward which go into that ward's transfer pool. If a party is too weak, it will gain votes from each ward's transfer pool in proportion to the number of transfer votes it needs over the whole old seat.

Party	General Election 2005 Votes	Local Election Turnout-adjusted Votes	Votes to transfer away	Votes to transfer into	Ward Transfers needed
CON	3,358	1,480	0	1,878	Transfer in 19.9% (= 1878 / 9457) of ward's transfer pool votes
LAB	19,687	15,616	0	4,071	Transfer in 43.0% (= 4071 / 9457) of ward's transfer pool votes
LIB	3,873	365	0	3,508	Transfer in 37.1% (= 3508 / 9457) of ward's transfer pool votes
NAT	3,947	10,275	6,328	0	Transfer away 61.6% (= 6328 / 10275) of ward's NAT votes
OTH	0	3,130	3,130	0	Transfer away 100.0% (= 3130 / 3130) of ward's OTH votes
Total	30,865	30,866	9,457	9,457

After transfer adjustment, the totals for each party over all the wards match the general election vote in the old seat.

Old seat: Caerphilly

					Actual Results					Turnout-adjusted Results						Transfer-adjusted Results
District	Ward	Electorate 2005	Old Seat	New Seat	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	Total Votes	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	Total Votes
Caerphilly	Aber Valley	4,909	Caerphilly	Caerphilly	0	2,310	0	2,142	351	0	1,349	0	1,251	205	2,805	347	1,635	209	585	26	2,805
Caerphilly	Aberbargoed	2,695	Caerphilly	Islwyn	0	967	0	430	242	0	908	0	404	227	1,539	169	1,048	102	189	29	1,539
Caerphilly	Bargoed	4,727	Caerphilly	Caerphilly	0	2,657	306	1,603	276	0	1,482	171	894	154	2,701	250	1,689	322	418	19	2,701
Caerphilly	Bedwas Trethomas and Machen	8,227	Caerphilly	Caerphilly	0	5,622	0	1,320	2,182	0	2,896	0	680	1,124	4,700	551	3,351	333	318	145	4,700
Caerphilly	Gilfach	1,680	Caerphilly	Caerphilly	0	674	0	115	0	0	820	0	140	0	960	30	845	18	65	0	960
Caerphilly	Hengoed	3,724	Caerphilly	Caerphilly	0	989	0	1,432	0	0	869	0	1,258	0	2,127	275	1,096	166	588	0	2,127
Caerphilly	Llanbradach	3,502	Caerphilly	Caerphilly	0	702	0	1,963	0	0	527	0	1,473	0	2,000	322	793	194	689	0	2,000
Caerphilly	Maesycwmmer	1,863	Caerphilly	Islwyn	0	531	0	154	0	0	825	0	239	0	1,064	52	868	31	111	0	1,064
Caerphilly	Morgan Jones	5,135	Caerphilly	Caerphilly	0	1,618	0	2,797	0	0	1,075	0	1,858	0	2,933	406	1,410	245	869	0	2,933
Caerphilly	Nelson	3,649	Caerphilly	Caerphilly	0	1,019	0	0	1,713	0	777	0	0	1,307	2,084	468	1,163	282	0	168	2,084
Caerphilly	Penyrheol	8,757	Caerphilly	Caerphilly	0	3,967	0	6,158	479	0	1,871	0	2,905	226	5,002	717	2,462	432	1,359	29	5,002
Caerphilly	St.Cattwg	5,764	Caerphilly	Caerphilly	0	2,981	0	0	3,105	0	1,613	0	0	1,680	3,293	602	2,110	363	0	217	3,293
Caerphilly	St.James	4,601	Caerphilly	Caerphilly	0	1,919	0	1,661	0	0	1,409	0	1,219	0	2,628	266	1,629	161	570	0	2,628
Caerphilly	St.Martins	6,058	Caerphilly	Caerphilly	1,447	1,732	1,343	2,146	0	751	899	697	1,114	0	3,461	994	1,100	844	521	0	3,461
Caerphilly	Ystrad Mynach	3,387	Caerphilly	Caerphilly	0	1,153	0	1,720	0	0	776	0	1,158	0	1,934	253	985	153	542	0	1,934
	Total		Caerphilly							751	18,096	868	14,593	4,923	39,231	5,711	22,190	3,861	6,831	636	39,231

The transfer table below shows the votes cast in the old seat of Caerphilly at the general election, as well as the total local turnout-adjusted votes. The number of votes to transfer, shown in the fourth and fifth columns, are the difference between the general and local votes. Strong parties will have votes transferred away, and weak parties will have votes transferred into them. The final column describes how votes will be transferred away from or into that party on a ward-by-ward basis. If a party is too strong, it will lose a percentage of its votes in each ward which go into that ward's transfer pool. If a party is too weak, it will gain votes from each ward's transfer pool in proportion to the number of transfer votes it needs over the whole old seat.

Party	General Election 2005 Votes	Local Election Turnout-adjusted Votes	Votes to transfer away	Votes to transfer into	Ward Transfers needed
CON	5,711	751	0	4,960	Transfer in 41.2% (= 4960 / 12047) of ward's transfer pool votes
LAB	22,190	18,096	0	4,094	Transfer in 34.0% (= 4094 / 12047) of ward's transfer pool votes
LIB	3,861	868	0	2,993	Transfer in 24.8% (= 2993 / 12047) of ward's transfer pool votes
NAT	6,831	14,593	7,762	0	Transfer away 53.2% (= 7762 / 14593) of ward's NAT votes
OTH	636	4,923	4,287	0	Transfer away 87.1% (= 4287 / 4923) of ward's OTH votes
Total	39,229	39,231	12,047	12,047

After transfer adjustment, the totals for each party over all the wards match the general election vote in the old seat.

New seat: Islwyn

District	Ward	Electorate 2005	Old Seat	New Seat	CON Votes	LAB Votes	LIB Votes	NAT Votes	OTH Votes	Total Votes
Caerphilly	Aberbargoed	2,695	Caerphilly	Islwyn	169	1,048	102	189	29	1,539
Caerphilly	Abercarn	3,669	Islwyn	Islwyn	90	1,650	168	283	0	2,192
Caerphilly	Argoed	1,989	Islwyn	Islwyn	47	902	89	149	0	1,189
Caerphilly	Blackwood	6,373	Islwyn	Islwyn	657	2,177	736	235	0	3,807
Caerphilly	Cefn Fforest	2,878	Islwyn	Islwyn	218	1,072	304	124	0	1,720
Caerphilly	Crosskeys	2,560	Islwyn	Islwyn	191	1,164	64	108	0	1,529
Caerphilly	Crumlin	4,496	Islwyn	Islwyn	184	1,575	345	580	0	2,686
Caerphilly	Maesycwmmer	1,863	Caerphilly	Islwyn	52	868	31	111	0	1,064
Caerphilly	Newbridge	4,870	Islwyn	Islwyn	404	1,614	331	557	0	2,909
Caerphilly	Pengam	2,986	Islwyn	Islwyn	173	1,235	176	199	0	1,784
Caerphilly	Penmaen	3,687	Islwyn	Islwyn	349	1,102	370	380	0	2,203
Caerphilly	Pontllanfraith	6,277	Islwyn	Islwyn	618	2,087	472	570	0	3,749
Caerphilly	Risca East	4,804	Islwyn	Islwyn	56	2,163	471	178	0	2,870
Caerphilly	Risca West	4,160	Islwyn	Islwyn	261	1,827	147	248	0	2,485
Caerphilly	Ynysddu	2,918	Islwyn	Islwyn	104	1,113	195	329	0	1,743
	Total			Islwyn	3,580	21,603	4,007	4,247	29	33,469

And these are the implied results for 2005 for the new seat of Islwyn.