Mr. Obama continues to get very strong results in state polls that use industry-standard methodology, meaning that they use live interviews and place calls to mobile phones along with landlines. In the 10 states that have generally been ranked the highest on our tipping-point list — Ohio, Virginia, Florida, Wisconsin, Colorado, Nevada, Iowa, Pennsylvania, New Hampshire and Michigan — there have been 21 such polls since the Democratic convention ended. Mr. Obama has led in all 21 of these surveys — and usually by clear margins. On average, he has held a six-point lead in these surveys, and he has had close to 50 percent of the vote in them. -Nate Silver