by Stephen Fisher

There was clearly a swing to the Republicans since 2012 in yesterday’s US midterm elections. However, the most comparable recent election for the House contest was not the general election but the 2010 mid terms.

The Democrats seem to have recovered votes since the 2010 big wave Republican takeover. According to yesterday’s exit polls, there has been a small (1 %) swing to the Democrats. And yet, the number of Republican House seats has increased from 242 in 2010, to a likely (at the time of writing) final tally of around 248 this year.

It could be that the exit polls are misleading regarding the overall share of the vote this year, but they would have to be quite far out to justify a 6 seat increase for the Republicans relative to 2010 given the general low responsiveness of US House elections to changes in vote share.

If the exit polls are not misleading, then the question is how can we explain Republican seat gains of Democratic vote gains since 2010?

Also, how come the Republicans can win 57% of the seats off a vote share than might be very close to, if not below, 50% of the vote?

The Republicans seem likely to end up with a 14% lead on seat share from just a 4% lead on vote or similar. If so then this suggests that both the combination of bias and responsiveness of the electoral system now strongly favours Republicans.

In 2008, when the Democrats last won the House their lead in votes was, at 10.6%, more than twice that for the Republicans this year, but their lead in seats, of 18%, was less than a third bigger the corresponding number this year. So the Democrats did not benefit in 2008 from such a strong votes-to-seats lead exaggeration that the Republicans have enjoyed this year.

The bias in the system is most clearly visible from the fact that in 2012 the Republicans won more seats even though the Democrats won the most votes.

It is also striking that the Republicans did not have such a strong advantage in 2004, when they achieved a much more moderate 6% seat lead from a 2.6% vote lead. Part of the reason for increasing bias in the electoral system for the Republican is their greater success in the redistricting process before the 2012 election.

The current overall electoral bias in favour of the Republicans and the advantages of new incumbency bonuses that they will accrue in 2016 together mean that it looks very difficult now for the Democrats to regain a majority in the House in two years time, even if they have a clear lead on votes.