Proof political journalists don’t understand opinion polls, No. 94

by Stephen Tall on March 10, 2008

Much scratching of heads tonight among some hacks confused by the latest Populus poll in The Times showing “the Tory poll lead shrinking fast”. Here’s Sky News’s Jon Craig:

Voting intentions, according to Populus, are now Conservatives 37 per cent (down three), Labour 34 (up three) and the Liberal Democrats 19 (up two, despite last week’s Lisbon Treaty vote shambles). That’s right, the same Populus poll on February 3 was Conservatives 40, Labour 31 and Lib Dems 17, a very different story. That was one of the bigger Tory leads in opinion polls this year.

Except it’s not necessarily “a very different story”. As any fule kno – or at least as any foolish hack should know – opinion polls are accurate only to within a margin of error, commonly +/-3%. Which means that it’s perfectly possible, and certainly statistically possible, there has been no change whatsoever in voting intentions in the last month.

But let’s allow for the possibility that there has been a significant change within the month… to what does Mr Craig ascribe this tightening of the political maths?

[Gordon Brown] has hired new staff in No 10 to beef up the Downing Street operation, he is performing better against David Cameron in Prime Minister’s Questions and he appeared more relaxed when he spoke at Labour’s spring conference in Birmingham 10 days ago.

Gordon’s backroom reshuffle, moderately better PMQs, and a conference speech. Apparently, according to Sky News, that’s what it takes to shrink a Tory poll lead. It says much (too much) about the claustrophobically introverted microcosm that political journos inhabit that any of these might seriously be put forward as reasons for the Tory downturn.