How election results are calculated and reported?
The Welsh Assembly's 60 seats are up for election on 5 May 2016. Here's what you need to know about how the election works and how the BBC reports the results.
How is the Welsh Assembly elected?
There are 60 seats in the Welsh Assembly.
Elected members, known as Welsh assembly members or AMs, are chosen using the Additional Vote System.
Voters have two votes each.
The first is used to select a constituency member to represent their local area. There are 40 constituency members, representing the 40 constituencies.
The second vote is used to elect four regional members, who represent the wider region in which the constituency lies.
There are 20 regional members for the five Welsh Regions.
Constituency members are elected using the "first past the post" system, where whoever gets the most votes is declared winner.
Regional members are elected using a form of proportional representation in which seats are allocated based on parties' share of the vote.
Major parties submit a list of candidates for each region and they are elected in order based on the number of votes the party receives.
The eventual number of seats awarded is adjusted to take into account the number of constituency seats that party has won in that specific region.
How do you win?
A party wins the election - and can form a government - if it wins more seats in the assembly than all the other parties put together.
There are 60 seats in total, so 31 seats are needed for a majority.
If no party wins a majority, the one with the most seats may try to form a coalition with one or more of the other parties.
Alternatively the largest party can form a "minority government" - and rely on the acquiescence or support of other parties in enacting its policies.
What is a constituency?
Also called a seat, constituencies are the election's political battlegrounds.
Although they vary in size geographically, they are all intended to contain roughly equal numbers of voters.
What is meant when a party wins, holds or gains a seat?
What matters most is how many seats each party wins, and for things to change political parties need to win seats from each other.
Because winning seats from each other is so important, a special language is used to show this. Seats that are won can mainly fall into two categories: "hold" or "gain".
Hold: If a party wins a seat that it won in 2011, this is described as a "hold".
Gain: If a party wins a seat that it did not win at the last election, this is called a "gain".
Win: Where there has been a by-election since the last election and that by-election resulted in a different party gaining the seat compared to the general election result.
For an opposition party to form a new government, they need to win seats from the existing government and other parties to make "gains", while they retain or "hold" all the seats they had last time.
Equally, incumbent governments will see to defend or even extend their mandate by holding all of their current seats, and gaining new ones from other parties.
What is a by-election?
By-elections are one-off elections in seats where, for example, the sitting AM has stood down or died.
There has been one assembly by-election in Wales since the last election, when Plaid Cymru's Ieuan Wyn Jones resigned to take up a role as head of Menai Science Park.
His seat was retained by Plaid Cymru.
The BBC ignores the results of by-elections to allow for a straightforward comparison with 2011's seats.
This is in recognition of the very particular circumstances which often surround by-elections.
Comparing seat change with the previous assembly election represents a fairer way of showing how the political expression of voters has changed.
What is a majority?
To achieve a majority a party must win one more seat than all the other parties added together.
Having a majority means a government can enact its policies more easily and without the need to forge alliances or rely on support from other parties.
The mixed member proportional representation system a means a majority is harder to achieve in the Welsh Assembly than at Westminster.
In the four elections since the assembly was formed no party has ever won an outright majority.
Which parties appear in the summary results graphic at the top of the results pages?
The results graphic always displays the top five or six parties in terms of seats won.
If more than six parties win seats, the parties with fewest seats are amalgamated into a grouping called Others.
In the event of a tie - eg. two parties have two seats - the party with the most constituency votes nationwide will be named.
After the first batch of results BBC analysts will be able to forecast how many seats the parties are likely to achieve overall.
This will be shown as grey shadow bars, marked as "Prediction", and may change as results unfold on election night.
Which parties are listed in the results tables?
To appear as a named party in the overall constituency seats scoreboard a party must
- Be fielding candidates in one-sixth of constituencies across Wales (7)
- Have achieved greater than 1% of the vote at the last Welsh Assembly election in constituency voting
- Had a sitting constituency member in the last assembly
Any parties which do not meet these criteria are amalgamated in a group called Others.
To appear as a named party in the overall regions scoreboard, a party or independent candidate must
- Be fielding 10 or more candidates
- Have achieved greater than 1% of the vote in the last election in overall regional voting
- Had a sitting regional member in the last assembly
Each individual constituency or region page will always name every party and candidate standing in that constituency or region.
What are the codes used for parties?
On smaller mobile screens, parties are sometimes abbreviated to 3 or 4 letter codes. Codes used in Wales are:
AWA: Abolish the Welsh Assembly Party
AWLI: Association of Welsh Local Independents
CS: Cymru Sovereign
CON: Welsh Conservatives
CPB: Communist Party of Britain
ED: English Democrats
GRN: Wales Green Party
ISW: Independent Save Withybush Save Lives
LAB: Welsh Labour
LD: Welsh Liberal Democrats
MRLP: Monster Raving Loony Party
PC: Plaid Cymru
PF: People First
SPGB: Socialist Party of Great Britain
TUSC: Trade Unionist and Socialist Coalition
UKIP: United Kingdom Independence Party
VIP: Vapers In Power
WCP: Welsh Christian Party
WEP: Women's Equality Party
Why does the postcode search not give the result I expect?
The postcode search box uses the latest available data supplied by Ordnance Survey.
Discrepancies can occasionally occur when a postcode search returns a different constituency to the one given on polling cards sent to an address at the same postcode.
Normally the constituencies concerned are next to each other, and it appears these discrepancies occur when postcodes are on the border between the two constituencies.
We would advise people affected to follow the information on their polling card in terms of the constituency they are in and the polling place to be used on 5 May.