Geographic Variation in Vote Change
The headline changes in share of the vote mask a substantial amount of variation between constituencies. This is one of the challenges of forecasting elections based on polls. In 2015, for example, the Conservatives national share of the vote rose by 0.75 percentage points. However, their vote share actually went down in 240 seats, including five were it fell by more than 10 points. Meanwhile, their vote share rose by more than 4 points in 145 seats. The dispersion of vote share increases has a profound impact on the seats won. More votes do not necessarily mean more seats won. In 2019 the Lib Dems added 4 points to their national vote share but ended up with one fewer seat.