Have the bookies adjusted for Ashcroft?

Last Wednesday social media was ablaze with Lord Ashcroft’s latest set of Scottish polls, which suggest that Labour are still on course for a Scottish wipeout on May 7. Has this affected what the bookies have to say?

As before, we look at mean implied probabilities for bookmakers, and this time consider the markets for banded ranges of seats for Labour. The impact of worse than previously anticipated polling in Scotland ought to be reflected in a lower seat expectation than previously. Betfair, Bet365, SkyBet, Ladbrokes and William Hill report markets on bands of seats a party wins at the election, and the bands are

  • less than 200 seats
  • 201-225 seats
  • 225 seats and under
  • 226-250 seats
  • 251-275 seats
  • 276-300 seats
  • 301-325 seats
  • 326-350 seats
  • 326 seats or over
  • 351-375 seats
  • 351 seats or over
  • 376-400 seats
  • 401 or more seats

Clearly the options towards the bottom of that range are hugely unlikely (bookies rate anything above 375 seats as less than 5% likely to happen), but it’s the upper half of the range when the action has been:

lab_bands

The black vertical line is March 4, when the Ashcroft Polls were released. Hence prices have moved since the announcement, but with the range 276-300 falling in likelihood only from 35% to 34% and 301-325 from 23% to 21%, the impact doesn’t appear to have been dramatic. Lower seat totals like 251-275 increased from 28% to 32%. Less likely events saw bigger moves, with 326-350 seats falling from 12.5% to 7% today.

Overall, the numbers would appear to suggest that the Ashcroft polls are reinforcing the current trends, at least in terms of bookmaker prices; an update to the plot of bookmaker implied probabilities for most seats from two weeks ago emphasises this:

most_seats_2015-03-09