House effects show how each pollster compares to the cross-pollster average. A positive (red) value means the pollster tends to put that party higher than average; negative (green) means lower.

Methodology: Each poll is compared with the average of the seven polls closest to it in time, so pollsters are measured against the state of polling when each poll was taken rather than a whole-window average (which would mix house effects with national movement over the window). A pollster's house effect is its mean deviation, re-centred so effects average zero across pollsters, giving equal weight to each pollster regardless of how often they poll. Only GB-wide polls count (UK-base polls and MRPs are excluded), and only pollsters with 5+ polls in the selected window are shown. The Overall Average row is the equal-weight mean of pollster average shares.