It’s always worth remembering that opinion polls are a snapshot, not a forecast –in other words that they only attempt to measure people’s preferences when they’re carried out not what will happen on Election Day.
Still, Dr Denis Balsom did well with his final projection last week for seats in the Assembly. He gave Labour 31 (they got 30), Conservatives 13, (they got 14), Plaid Cymru 11 (spot on) and Lib Dems 5 (also spot on).
Of course, that one seat has made all the difference to Labour as it faces having to govern either without a majority or after doing a deal with another party. So what made that difference? Almost certainly it came down to turnout.
Our YouGov poll results were weighted for likelihood to vote but sadly not everyone who thinks they are certain to vote actually does so –it’s particularly true at Assembly elections and traditionally particularly true of Labour voters.
Labour campaigners felt that was less the case this time than at previous Assembly elections. In the past, many of the party’s supporters were annoyed with Tony Blair or Gordon Brown. But there were also specific reasons why the other parties’ supporters were more likely to actually make it to the polling station. Plaid Cymru supporters are the most likely to take an Assembly election seriously, Conservative supporters also tended to feel strongly about voting ‘no’ in the AV referendum and Lib Dem support was down to its hard core –or at any rate mostly hard core enough to vote.
One off polls can be wrong but successive polls tend to give a pretty accurate picture. YouGov consistently found Labour support in the high forties for the constituency vote and in the low forties for the regional vote, yet they finished on 42% in the constituencies and 37% in the regions.
The Conservatives moved above the 20% they had been polling to get 25% in the constituencies and 23% in the regions. As well as the AV referendum factor, they seem to have picked up some people who had been minded to vote for UKIP. Plaid Cymru and Lib Dem support was much as the polling suggested.
YouGov have also released some experimental polling that they did on Election Day itself (as an internal exercise for themselves, not for ITV Wales).