FPTP Breakthrough

[Raddy]

I'm sure it has been discussed to death over the years, if so can somebody point me in the direction of where to find it

If not, what is the notional breakthrough share required for a party like Reform with highish support in England and Wales with low support in Scotland and Northern Ireland, or the Greens with level support across the country.

Thanks in advance.

[Crimson King]

I would think that is almost impossible to determine. If it were the case that the distribution of votes in constituencies varied in some predictable way around the mean national vote (which it doesn’t) and you knew that distribution, (which you don’t) it would be possible to calculate how many seats would be above a specific vote level, but whether that was a winning share and thus a ‘breakthrough’ would depend on the performance of the other parties in each constituency, which would have the same problems in determining.

[nodealbrexiteer]

Apr 6, 2024 8:24:20 GMT Crimson King said:

I would think that is almost impossible to determine. If it were the case that the distribution of votes in constituencies varied in some predictable way around the mean national vote (which it doesn’t) and you knew that distribution, (which you don’t) it would be possible to calculate how many seats would be above a specific vote level, but whether that was a winning share and thus a ‘breakthrough’ would depend on the performance of the other parties in each constituency, which would have the same problems in determining.

I remember seeing some work on a similar matter in a 1980s book on proportional representation which showed assuming UNS some scenarios of the Alliance taking votes from the other 2 parties and then 'taking off' seat wise at a 40% plus figure. With i believe the Tories falling to 3rd place in seats despite being 2nd in votes!

[johnloony]

17.38%

[The Bishop]

IIRC there was a poll in autumn 1985 that had shares of Lib/SDP 36 Lab 32 Con 30 or similar - it was mentioned this was near to the "tipping point" where the "Alliance" (as we called them back in those fondly recalled days) would abruptly turn FPTP to their advantage and win loads of seats.

[Crimson King]

Indeed, but that was a particular party with known numbers for the other parties. Not the same as a general rule for “a party like reform”
in the case of the Greens, one could argue that the breakthrough has already been made despite a lowish and evenly spread poll rating because of local campaigning

[Harry Hayfield]

At the February 1974 general election, a chart was shown showing the number of seats that could be won by the Liberals on an increasing vote share in Britain from a base of 8% for the Liberals

Liberals: 10% = 10 seats, 20% = 20 seats, 25% = 50 seats, 30% = 150 seats

Therefore it could be argued that for a smaller party such as the Greens, they would need 10% across the UK to win more than 1 seat, and for Reform UK closer to 15%

[nodealbrexiteer]

Apr 6, 2024 15:06:53 GMT Harry Hayfield said:

At the February 1974 general election, a chart was shown showing the number of seats that could be won by the Liberals on an increasing vote share in Britain from a base of 8% for the Liberals

Liberals: 10% = 10 seats, 20% = 20 seats, 25% = 50 seats, 30% = 150 seats

Therefore it could be argued that for a smaller party such as the Greens, they would need 10% across the UK to win more than 1 seat, and for Reform UK closer to 15%

Was the chart shown on the BBC coverage that we can see on Youtube?

[uthacalthing]

It depends who you are taking votes from, who else is taking them from them, who they are taking them from, who else is taking votes form who else, who else is losing them to who else and where all of this is happening

For example, when the SNP took votes mostly from the Conservatives they peaked at 12 seats out of 72 on about 30%. When Scottish Labour took votes mostly from the Conservatives they peaked at 50 out of 72 on about 40%

The Lib Dems, taking votes mostly from the Conservatives, would be lucky to get 50 seats on 20% of the vote if the Tories dropped to 30%, but if they got 30% and the Tories dropped to 20% the Lib Dems would take 200.

Reform will be lucky to get 3 if they get 15% nationally but if they get 25% they might well get 50.

Labour on 40% might get 350 if the Tory vote firms up, or 450 of the Tory vote is fractured

[nodealbrexiteer]

Apr 6, 2024 15:28:28 GMT uthacalthing said:

It depends who you are taking votes from, who else is taking them from them, who they are taking them from, who else is taking votes form who else, who else is losing them to who else and where all of this is happening

For example, when the SNP took votes mostly from the Conservatives they peaked at 12 seats out of 72 on about 30%. When Scottish Labour took votes mostly from the Conservatives they peaked at 50 out of 72 on about 40%

The Lib Dems, taking votes mostly from the Conservatives, would be lucky to get 50 seats on 20% of the vote if the Tories dropped to 30%, but if they got 30% and the Tories dropped to 20% the Lib Dems would take 200.

Reform will be lucky to get 3 if they get 15% nationally but if they get 25% they might well get 50.

Labour on 40% might get 350 if the Tory vote firms up, or 450 of the Tory vote is fractured

11 seats?

[michaelarden]

It depends on the number of parties. Getting 49% in a two horse race will see you win zero, but with a third party getting 2% it will see you win everywhere. I suspect the old calculations of 35% plus to get to a tipping point is significantly lower now, especially with all parties (with the possible exception of Reform) understanding local campaigning in a way they didn't previously.

[Harry Hayfield]

Apr 6, 2024 15:22:23 GMT nodealbrexiteer said:

Apr 6, 2024 15:06:53 GMT Harry Hayfield said:

At the February 1974 general election, a chart was shown showing the number of seats that could be won by the Liberals on an increasing vote share in Britain from a base of 8% for the Liberals

Liberals: 10% = 10 seats, 20% = 20 seats, 25% = 50 seats, 30% = 150 seats

Therefore it could be argued that for a smaller party such as the Greens, they would need 10% across the UK to win more than 1 seat, and for Reform UK closer to 15%

Was the chart shown on the BBC coverage that we can see on Youtube?

Yes, it is indeed, around 1.30am in the morning.

[hullenedge]

An equivalent diagram the late Michael Steed plotted for 1979:-

[hullenedge]

And the notes:-

[Raddy]

Fascinating, many thanks to all those who responded.

Even with only one third party polling well, we don't appear to really know really know the share required to breakthrough in seats. With the Greens, LibDems and Reform all theoretically maintaining their current polling figures of collectively around 30%, could we be in for a surprise, especially if Labour falls back somewhat nearer the date.

[johnloony]

Apr 6, 2024 20:37:20 GMT hullenedge said:

And the notes:-

The third line in that table has a misprint of 39.0 39.0 which should be 37.0 37.0

Whoever photographed those pages (apparently with a phobile moan) is a booliak for not taking measures to avoid the ghastly shadow

[uthacalthing]

In any case, the scenario of the Lib/SDP taking votes almost equally from Labour and Conservative while both of them go backwards in roughly equal measure gives little guide to how Reform would do taking votes overwhelmingly from the Conservatives while Labour go forward

The reality is that even if Reform went ahead of the Conservatives what would happen is that Labour would win more seats. Reform would need to get close to or overtake Labour before they win significant numbers. Once we have a two and four half-party system (Labour, Reform, then Rump Tory, Lib Dem, Green plus Celtic separatists) we might see Reform get above 100 then leap quickly to 200.

Don't hold your breath

[hullenedge]

x.com/OwenWntr/status/1780889919952425287

x.com/OwenWntr/status/1780892605976330392

Three interesting(?) graphs.