Are there house effects in Swedish polls? A compositional approach

Abstract

 We investigate if we can find evidence of house effects in Swedish political opinion polls from 2006 to 2014. In order to respect the inherent restriction of the simplex sample space, we apply compositional data analysis and Aitchison geometry. We use compositional locally weighted regression (C-loess) to estimate the share of voters for each party at given dates, a poll of polls. The estimated shares are compared to the poll(s) for that date using simplicial distances and compositional deviations (inverse perturbation). We can conclude that neither the mean simplicial distance nor the mean compositional deviation are equal for all polling organisations, also when controlling for different sample sizes and limiting the sample to only the last two years.