Is Obama’s big lead in Bloomberg poll to be believed?

WASHINGTON -- Most national polls continue to show President Obama and Mitt Romney neck and neck. So how does one explain a new Bloomberg survey that shows the incumbent 13 points ahead of his GOP rival?

That poll, conducted by the respected Iowa-based Selzer & Co. from June 15-18, gives Obama a 53% to 40% lead among likely voters, with 5% of respondents undecided.

And there’s plenty more to like if you’re an Obama backer. By a 19-point margin, voters say Romney is more out of touch with average Americans than Obama. Voters give a slight edge to the president on getting the economy going, and 49% say he has laid out a better vision for the nation’s successful economic future.

Obama supporters also tended to be more enthusiastic about their candidate, and a slight plurality of voters say they are better off now than they were four years ago, a key question in any reelection year.

The survey was in the field over the weekend, on the heels of Obama’s announcement that he would halt deportations for young illegal immigrants, and as Romney was on a bus tour through key battleground states. The sample of 734 likely voters has a margin of error of 3.6%.

Political polling is always a bit of a guessing game. In compiling the data, pollsters weigh the results based on their best guess as to what the electorate will look like Nov. 6.

One clue as to why Bloomberg’s results may be an outlier is in their voter breakdown. One-third of the sample is non-white voters, including 12% black and 11% Hispanic.

Other surveys tend to include a somewhat smaller percentage of minority voters. In fact, when Gallup’s first daily tracking poll of the Romney-Obama matchup showed the former Massachusetts governor several points ahead, Obama advisors noted that Gallup had, in their view, under-valued the minority vote -- 22%.

Exit polls in 2008 found that 26% of the electorate was non-white, and that vote went overwhelmingly to Obama over John McCain.

The most recent three-day Gallup tracking poll showed Romney at 46%, Obama at 45%.

So, while the Bloomberg results are instructive, it’s best as always to keep an eye on the trend lines within individual polls, rather than draw major conclusions from a single one.

michael.memoli@latimes.com