It is widely known that pre-electoral polls often suffer from non-sampling errors which
pollsters try to compensate in final estimates by means of diverse ad hoc adjustments, thus leading to
the well-known house effects. We analyze vote share predictions from election polls in Italy in 2006,
2008 and 2013 in order to investigate the relative role of house effects on their variability. We are able
to confirm that the variability due to house effect is the most important source of variation
