I’ve previously talked about the accuracy, or not, of the Thrasher and Rallings prediction for the Lib Dem vote share in local elections, but what about the other parties?
Today then, let’s look at their record for Labour in vote share* predictions based on by-election results in advance of the big May round of elections.
|Forecast Labour %||Actual Labour %||Error in forecast|
Unlike the consistent over-estimation of the Lib Dems, for Labour these predictions have a lot more variation, including a spectacular failure in 2013 where the Ukip surge hit Labour badly and less strikingly in 2017 when Labour outperformed the forecast even before the big Corbyn general election surge.
To see the full context of the predictions and results each year, see my PollBase collection of local election results.
* Different rounds of seats are up for election each year, so Thrasher and Rallings calculate a national equivalent vote, which adjusts for this and therefore make possible like-for-like comparisons between different years. The intent is the same as for the separate BBC / Curtice and Fisher calculations, though following a different methodology and hence also usually producing slightly different results. The fact that however they both, with their own different approaches to the issue, consistently produce the same trends and overall picture – e.g. this time Lib Dems moving back above Ukip – is a good sign that the pictures they paint are right.