Combination of sample surveys and projections of political opinions
(English)Manuscript (preprint) (Other academic)
In Sweden, political party preferences are surveyed almost every month by several institutes. The sample sizes are usually between 1000 and 2000 individuals, which means that the standard deviations are between 1 and 1.5 %. We study how these estimates can be improved by combining them and by modelling the behaviour over time. Our model is a combination of a dynamic model based on Wiener processes and sampling theory with design effects and measurement biases. The variances of our estimates are about 1/3 of those of the original polls when only previous polls are used and about 1/5 if the information in later polls is included. The proposed method leads to a smaller bias since the institute biases can be estimated. The party preferences are modelled as random processes, making it possible to study the probability for events like a party (or block) getting more than 50 % of the political preferences. Assuming that the same model will hold in the future, we can present intervals for future election results.
Probability Theory and Statistics
IdentifiersURN: urn:nbn:se:su:diva-89314OAI: oai:DiVA.org:su-89314DiVA: diva2:617057