Polling in 1979–83 and The Alliance

If history is our guide, then we should remember well. Some political commentators have claimed that the SDP-Liberal Alliance were at 50.5% “in the polls” in 1981 — when only one poll had such a share.

This article looks at Westminster voting intention polls in the 1979–83 Parliament.

In short

“In the polls”: If a statement talks about a party’s vote intention share ‘in the polls’, then the claim should be accurate for averages of polls — not just one.

Well-tracked: the rises and falls of The Alliance’s vote intention share were well-tracked by polling. Averaging the final polls showed a 4.6 point error for the Conservative-Labour lead.

The past’s faulty guide

The splinter parliamentary grouping of breakaway Labour and Conservative MPs, called The Independent Group, are somewhat analogous to the Social Democrat Party established in 1981.

Four well-known Labour figures (Bill Rodgers, Shirley Williams, Roy Jenkins and David Owen) were disaffected with their party’s direction. This group, known as the Gang of Four, proposed the Council for Social Democracy, which became the Social Democrat Party. By June 1981, the SDP had formed an electoral alliance with the Liberals.

With any historical analogy, our memories may not so be accurate.

“In the polls”

Owen Jones, columnist for The Guardian, claimed that the SDP “reached 50.% in the polls”.

Iain Dale, an LBC radio presenter, suggested that the SDP had reached a vote intention share of 50% “within a week” of launching.

Neither of these claims is accurate. It is worth examining what vote intention polls actually showed during that Parliament.

One poll — conducted by Gallup for the Daily Telegraph, between 9th and 14th December 1981— did show the SDP-Liberal Alliance on 50.5%. This vote intention share was 27 points ahead of Labour in the same poll.

However, this single point estimate of the Alliance’s support was sharply different to other polls around that time, even by the same polling company.

Seven polls showed the vote intention share for the Alliance at 40% of more, all between October 1981 and January 1982. No other polls showed the SDP-Liberal Alliance at more than 45%. Gallup’s November 1981 poll had the Alliance at 42%, whilst their January 1982 reading put the pact on 39.5%.

Focusing on a single poll — which was particularly memorable — is inaccurate when stating how the parties were “in the polls”. It is also likely to give a misleading impression of public opinion at that time.

Nor did the party begin reaching such highs in opinion polls quickly. It took several months after the Limehouse Declaration and the announcement of the pact for the new party to record polling leads.

Support for the SDP-Liberal Alliance subsided irregularly after December 1981, before rising again during the 1983 General Election — approaching the Labour share.

Final polls

Using Mark Pack’s polling database, the five final polls (which included 8th June 1983 in their fieldwork) all showed the same share for the Alliance: 26%. As it happens, the Alliance’s share of votes cast in Great Britain was 26.0%.

Given this support was widely dispersed, the electoral system — where every MP is elected by a local contest — meant the SDP and Liberals had only 23 MPs.

The average of these five final polls overestimated the Conservatives by 2.4 points, and underestimated Labour by 2.2 points. The average final poll had a 4.6 point error in the Conservative lead.

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.