A MORI poll conducted for the Observer shows the Labour Party gaining five points, narrowing the Conservative Party’s lead to six points. The shock results have offered succour to the Labour Party and its supporters, and has even prompted political pundits to pen columns outlining the implications of a hung parliament.

This is understandable. Any shift as large as MORI’s is likely to cause a stir among the political wonks and talkingheads, and it comes hot on the heels of the ICM data for the Guardian which also showed Labour gaining (albeit by only 2 points), suggesting a trend.

However, the Parallax Brief believes it is far too early to start talking of a hung parliament. First, one must account for differences in polling methodology. MORI’s polls are generally liable to produce more violent swings, and there is genuine reason to believe that this particular poll was simply taken from a sample of people more likely to vote Labour.

The excellent UK Polling Report blog has more:

…the big difference between MORI and other pollsters is that MORI do not politically weight their sample. All the pollsters including MORI weight their samples by known demographic figures like age, gender, social class and region. All except MORI also use political weighting, normally weighting by how people claim they voted at the last election.

… people aren’t very good at recalling their 2005 vote. ICM, Populus and ComRes take the view that past recall is pretty stable over time and can be estimated well enough to weight by, MORI take the view that it’s too unstable and should not be used for weighting. The result is that MORI’s samples run the risk of varying politically from month to month more than those of other companies (though MORI would claim the opposite – that other companies risk weighting out genuine public volatility).

MORI’s poll last month which showed a 17 point Tory lead, amongst those who voted in 2005 32% said they voted Conservative, 43% Labour and 16% Liberal Democrat. In this month’s poll which shows a 6 point Tory lead the figures of recalled 2005 vote break down as Conservative 29%, Labour 46% and 16% Liberal Democrat – so a 6 point change in the recalled lead from 2005.

The MORI polling data for the last several years gives an impression of the month-to-month volatility:

Meantime, Mike Smithson at Political Betting notes that the poll has hardly moved the spread betting lines at all, with sporting index pushing down the Conservative seat spread to 353-357, and Labour up to 208-213. Betfair has seen similarly slight movement (as indicated in the chart below). Those who believe in the efficiency of markets, or the effectiveness of the wisdom of crowds to out-predict the experts, should take note.

Further, Mr Smithson notes that both the MORI and ICM polls were undertaken shortly after Labour’s Glasgow North East by-election victory, which suggests the party gained from the brief surge of positive publicity which always comes with a by-election victory.

Of course it is true that not all the six point swing can be accounted for by MORI’s methodology, and that irrespective of mitigating factors such as timing, these are two great polls for a beleaguered Labour Party; however, those talking of a hung parliament need to wait to see if the next poll posts numbers that might suggest the beginning of a trend, or at least that public opinion has undergone a correction to a new normal, before talking of a hung parliament.