Pollsters join Democrats as big losers
The polls were off in Maryland by 20 points: Hogan won by 10, and polls showed him behind by 10. The Virginia Senate race off by 10.
On average, GOP candidates beat polling average by 5 points in close Senate races, and by 3 in close governors’ races – almost the reverse of 2012, when Dems over-performed.
Midterms in general are off by more than polls in presidential years. Pollsters always adjust their raw results to achieve mixes of Dems and Republicans, various age groups, parts of a state, etc. Those adjustments suggest that patterns are fixed – but they are not.
Republicans over-polled for a few cycles, because cell phone users were undercounted. It is possible that the adjustment for that this time was too high in an off-year, with higher GOP enthusiasm.