The Altervative Vote (AV) system is a little more complicated. The basic idea is that voters rank candidates in order of their preference. If a voter's most favoured candidate is not popular, then the vote is transferred to the voter's second favourite candidate, and so on. The rules of the system are these:
The AV system can be good for voters who have a preference for more than one candidate (eg a Lib Dem supporter who also likes Labour, or a UKIP supporter who also likes the Conservatives). If the voter's first preference candidate does not succeed, then the voter's second (or further) preference will be used. The AV system is not so good for voters who only like one of the candidates.
From the candidates' point of view, AV is good if the candidate appeals at least partly to many voters, even if only a few are strongly attracted. Conversely, AV is bad for a strong candidate who has several (divided) opponents.
Bristol North West
County/Area: Bristol area (West)
MP: Charlotte Leslie (CON)
|2010 Votes||2010 Share|
Suppose the AV system had been in use at this election. What would the result have been now?
In fact, the "Other" party is actually the total of three parties (UKIP, English Democrats, and the Greens) rather than one single party, but the net effect is the same.
The transfer amounts come from the table in the section below. For example, the Conservatives receive 2,321 x 21.8% = 505 votes from the Others.
So under AV, the Liberal Democrats win this seat rather than the Conservatives. This is because Labour was in a strong third place, and Labour votes greatly prefer the Lib Dems as their second preference rather than the Conservatives.
To do this, we need to know what voter's second preferences are. Peter Kellner at YouGov has kindly provided Electoral Calculus with polling results on this question. The poll was conducted just before the May 2010 general election, so it should be a relatively good guide to voters' intentions.
|May 2010||Second choice|
Each row of the table corresponds to the first-preference supporters of each party. For example, the first row corresponds to voters whose first preference is the Conservative party. The percentage numbers in that row indicate the second preferences of those Conservative supporters. For instance, 4.9% of first-choice Conservatives will switch to Labour for their second choice, and 46.0% of them will switch to the Liberal Democrats as their second choice.
This shows us that Conservative voters tend to give their second preference support to the Liberal Democrats rather than to Labour. Similarly, Labour voters also give their second preference votes to the Lib Dems (65.2%) rather than to the Conservatives (6.2%). Liberal Democrat voters are more evenly split, but generally favour Labour (42.8%) over the Conservatives (28.4%).
The pie-chart (see right) gives a graphical view of these preferences. The outer ring
consists of voters' first preferences - 37% support the Conservatives, 30% support Labour
and 24% support the Lib Dems. The inner ring shows the second preference of the voters.
We see that Conservative supporters mostly give their second preference to the Lib Dems
(pale yellow slice, labelled ConLib) or
Other (biege slice, labelled ConOth), which includes "Don't Knows" or no further preference.
There is only a
thin slice of Conservative supporters who will transfer to Labour (pink slice, labelled ConLab).
Labour voters mostly switch to the Lib Dems or Other, but Lib Dem voters can go to the
Conservatives, Labour or Other.
Given those caveats we can calculate the result of each election since 1983 under both FPTP and AV:
|Jun 1983||FPTP||397||209||23||4||17||Con majority of 144|
|AV||347||224||59||3||17||Con majority of 44|
|Jun 1987||FPTP||376||229||22||6||17||Con majority of 102|
|AV||333||237||59||4||17||Con majority of 16|
|Apr 1992||FPTP||336||271||20||7||17||Con majority of 21|
|AV||298||288||42||4||19||Con short 28 seats of majority|
|May 1997||FPTP||165||419||46||10||19||Lab majority of 179|
|AV||112||426||93||9||19||Lab majority of 193|
|Jun 2001||FPTP||166||413||52||9||19||Lab majority of 167|
|AV||138||416||81||5||19||Lab majority of 173|
|May 2005||FPTP||198||356||62||9||21||Lab majority of 66|
|AV||164||358||98||5||21||Lab majority of 70|
|May 2010||FPTP||307||258||57||9||19||Con short 19 seats of majority|
|AV||268||258||97||6||21||Con short 58 seats of majority|
We can see that generally AV is fairly bad for the Conservatives, very good for the Liberals / Liberal Democrats, and mildly good for the Labour party. However, most election results are not actually changed by using AV. But there are two main exceptions:
However, with AV the Conservatives would not have had an overall majority. They would have been the largest party with 298 seats out of 651, and Labour would have been close behind with 288 seats. The newly-formed Liberal Democrats, led by Paddy Ashdown, would hold the balance of power. A Conservative/LibDem coalition would have a majority of 29 seats, but a Labour/LibDem coalition would also have a majority of 9 seats.
It cannot be certain what Mr Ashdown would have decided to do. But his later efforts to form an alliance with Tony Blair suggest that he could have been very open to a coalition with Neil Kinnock in 1992. History would have been very different if John Major had lost to a Labour/LibDem coalition, which would then have faced the coming financial crisis.
However, under the AV system the parliamentary calculus would have been quite different. The Conservatives would have only won 268 seats (58 seats short of a majority), with Labour just 10 seats behind that. A Con/Lib coalition would have a majority of 80 seats, but a Lab/Lib coalition would also have had a comfortable majority of 60 seats.
If a party has a relative ratio of more than 100%, this means that it needs more votes to win each seat than Labour does. If its relative ratio is less than 100%, then it needs fewer votes. If the relative ratios are around 100%, then the voting system is approximately proportional. The graph shows the relative ratios for the Conservatives and Lib Dems under both FPTP and AV for the elections between 1983 and 2010.
The following points appear from these data:
The graph on the right shows the breakeven gap for each election from 1983 to 2010, under both FPTP and AV systems. A gap of 0% is "fair", with a negative gap being favourable to the Conservatives (as in 1983 and 1987 under FPTP) and a positive gap being favourable to Labour (as in 1992 to 2010).
We see that, according to this measure, the AV system actually increases unfairness. In six of the seven elections, the size of the gap increases, which indicates the electoral landscape is less "fair". Only in 1987 does the gap size decrease, and then only slightly (from -3.9% to +3.5%).
This unfairness of AV between Labour and the Conservatives reflects the relative Vote/share unfairness that we saw above.
Perhaps this should be balanced with the increased fairness which the AV system gives to the Liberal Democrats.
|July 2010||Second choice|
These new data show that the remaining Liberal Democrat supporters are now more likely to favour the Conservatives (36%) over Labour (32%) with their second preferences. But Labour voters are confused and are now less likely to make the Lib Dems their second choice. Conservative voters are relatively unchanged, though slightly more supportive of Lib Dems.
Since the forming of the coalition government, it seems that Labour-leaning Liberal Democrats
have abandoned the party and switched their support to Labour directly. The remaining Lib Dem supporters
are more Conservative-inclined, and might be assumed to be natural coalition supporters.
Many Labour voters are confused by the formation of the Conservative/Liberal coalition, because they
used to see the Liberal Democrats as left-leaning. The percentage of Labour voters whose second choice
is the Lib Dems has plummeted from 65% to 37%. Most Labour votes now prefer minor parties or "Don't Know" (52%).
At the current time (December 2010), headline Labour support has increased to 40% and the Liberal Democrats have decreased to 10%. We are not aware of any second preference polling since July 2010, but it might be expected to mirror the headline trends.
The new AV prediction feature (user prediction, choose Voting System = "Alternative Vote (AV)") uses the July 2010 matrix of second preferences shown above.