Guest Pollster Nick Panagakis is president of Market Shares Corporation, a marketing and public opinion research firm headquartered in Arlington Heights, Ill.
The National Council on Public Polls analyzed national presidential poll accuracy In 2004. The found that eleven of fifteen pollster margins were off by 0% to only 2% from the winning margin., well within the margin of error.
This year polls are now showing Obama from +5 points to +13 ahead, more variability than four years ago this week. This year a demographic variable appears to be having an acute effect on voting estimates. That variable is race and may explain the difference in poll margins.
I did a "what if" spreadsheet analysis with hypothetically variable percentages of black composition of total voters and corresponding variable percentages of the white/other races of turnout. I set a constant result for the vote for president by African-Americans.
Typically, polls lack sufficiently large samples of black voters to reliably estimate their voting intentions. I derived my estimate from a tracking poll's pooled results: 95% of African-American would vote for Barack Obama, 3% for John McCain and 2% for other candidates. A one or two point disparity from 95% for Obama doesn't make much difference in this analysis. If anyone has better results, please respond to this column.
The key variables are the racial distribution of voters and how white/race voters will vote.
Exit polls in the last few elections have shown African-American varying from 10% to 12% (in 2004) of total voters. My analysis ranged from 10% to a hypothetical 15% to check incremental margin gain.
General voter interest in this election may be so high, black composition could remain at 12%. But if it increases to 13%, that adds a one-point margin gain for Obama. For each one percentage point increase in black composition, the overall margin for Obama increases by one percentage point.
The other variable is how whites and others would vote. The following hypothetical scenarios cover most of the overall margins current polls are showing. They range from +4.8 to +9.4 Obama winning margins.
Assuming McCain is ahead by 7 points among whites/others and with 12% African-Americans of all voters, overall results are a Obama win of +4.8%. At 13% black voter of total turnout this would result in a +6.0 point Obama win.
Assuming McCain ahead by only 5 points among whites/others and with 12% African-American sample composition. This would yield an Obama win of +6.6 points. At 13% black voter composition results are a +7.6 point Obama win.
Assuming McCain down to +3 points among whites/others and with 12% black voter sample composition. This would yield an Obama win of +8.4 points. At 13% black voter composition results in a +9.4 point win for Obama.
In closing this analysis has nothing to do with the Bradley Effect theory. And nothing to do with reverse-Bradley. (Since when can a theory have it both ways?) Pre-election poll versus exit poll or post election analysis examining such variables could have confirmed or denied the effect.