Forecasting the 2010 general election using aggregate local election data

The paper presents a revised method for estimating national vote shares using aggregate data from local government by-elections. The model was originally developed to forecast the annual outcome of local elections but was adapted in time to provide an accurate forecast of Labour’s landslide victory at the 1997 general election. However, over the past decade the changing pattern of party competition which has seen parties becoming more selective about which elections to contest has led to more elections being excluded from the modelling because they failed to meet the exacting criteria that all three major parties, Conservative, Labour and Liberal Democrats, had contested both the by-election and the previous main election, normally held in May. Relaxing these criteria, although increasing the number of available cases would adversely affect the forecast, over- or under-estimating party votes. Instead, the revised method overcomes the problem of differential competition by estimating vote shares for parties that contest one but not both elections. A further innovation is the calculation of a weighted moving quarterly average which takes account of the number of days elapsed between the by-election date and the date of forecast. Using the new method we provide estimates for likely party shares for the 2010 general election.     

Forecasting the 2015 general election using aggregate local election data

Local government election results are used to estimate a national equivalent vote that provides the basis for a general election forecast. By-elections provide the means for calculating weighted quarterly averages of national support. These show trends similar to those obtained by national polls. By-election results in the three month period leading to the general election contribute towards the national vote share calculation and seat distributions are determined by uniform national swing. Additionally, results from the main council elections from 2011 onwards are aggregated to the parliamentary constituency level and used to estimate each party's relative performance in key target seats. This information is used to fine-tune the final seat forecast which suggests a hung parliament is the most likely outcome.     

The Maltese general election of 1987

The Maltese general election of 9 May 1987 returned the Nationalist Party to power with a single-seat majority in Malta's unicameral legislature. The result, on a record 96.11 per cent poll, ended sixteen years of Malta Labour Party rule. In the 1981 elections the MLP had gained a majority of seats—34 to the PN's 31—despite polling a minority of votes in the islands' complex STV system. Constitutional changes passed by Parliament in January 1987 ruled out the possibility of such a ‘freak’ result being repeated, by guaranteeing the party polling a majority of votes a majority of seats through a ‘topping-up’ procedure. This change gave the Nationalists victory in 1987. Early stages of the lengthy campaign witnessed fairly serious political violence, and fears had been expressed that in May whoever lost might refuse peacefully to concede defeat. However, whilst polling day and. more particularly, the aftermath of the result were marked by some violent incidents, the transfer of power from Labour to the PN took place smoothly. Maltese democracy, often seen as fragile by outside observers, seemed to have passed this difficult test.