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 Pollster Peter Kellner argues the reverse Bradley effect could apply to the US election results as people who have never voted before turn out.
In polling, as in so much else, the United States
does not do things by halves, writes Peter Kellner. "Every day brings a slew of new polls, both
national and at state level, on the race for the White House. As statistical
theory would predict, they do not all agree on the numbers.
Recent Obama
polling leads range from two points to 14. What they have all agreed for the
past six weeks is that Barack Obama leads not only nationally but in most of
the battleground states that will determine the outcome.
However, some Democrats fear, and
Republicans hope, that the polls may be wrong: that they may be overstating
Obama’s support because some voters are telling pollsters that they will vote
for him when, in fact, they will vote for John McCain or not vote at all.
However, pollsters and pundits are divided on this, as I discovered last week
on a visit to Palo Alto, California, home of YouGov-Polimetrix (whose clients
for the US elections include the CBS television network) and Stanford University’s
Hoover Institution (which houses some of the country’s best political
scientists and which invited me over for the week).
Indeed, there is one school of thought that
argues that the polls may be wrong for the opposite reason – they might be
UNDERSTATING Obama’s support.
Here are the arguments put forward by the
two opposing camps.
First, the reason why Obama’s lead might be
overstated. It’s down to the ‘Bradley Effect’. This is named after Tom Bradley,
who stood for Governor of California in 1982. He was ahead in the polls, but
ended up losing. Some believe that he suffered because he was black – and some
voters lied to pollsters, saying they would vote for him when because they were
unwilling to admit their racism and their intention of voting for Bradley’s
white opponent. (It’s important to note that the ‘Bradley effect’ is about
polls, not general voting behaviour. There is no ‘Bradley effect’ where people
vote against black candidates because of their race, and are happy to tell
pollsters their true intentions.)
The ‘Bradley effect’ has been observed on a
number of occasions since. Some observers attributed Obama’s defeat to Hillary
Clinton in the Democratic primary nine months ago to the Bradley effect. If
that is right, then the possibility that it might be distorting the polls in
the current presidential race can’t be ruled out.
What, then, is the evidence? There are
certainly some instances where pollsters have overstated the support for black
candidates. There are, though two ‘buts’. The first is that Bradley himself may
NOT have been a victim of the effect that bears his name. The daily tracking
polls by Tarrance and Associates showed the race narrowing week by week during
the campaign, from 12 points with a month to go, to one point in their final
poll. Bradley’s narrow defeat could simply have been a continuation of that
trend.
So why did the ‘Bradley effect’ gain such
prominence? Because another pollster, Mervin Field, showed Bradley seven points
ahead on the final weekend; an exit poll he conducted on election day also
showed Bradley ahead. After the election he sought to explain his error. He
said ‘race was a factor in the Bradley loss’. On the other hand, it could be
that Bradley’s final campaign poll was not as good as Tarrance’s. As for the
exit poll, Field failed to take account of postal votes, which went
overwhelmingly to Bradley’s opponent, George Deukmejian. Bradley did, in fact,
‘win’ the votes cast on the day.
However, even if the ‘Bradley effect’ did
not apply to Bradley’s own election, it does seem to have applied to a number
of contests in the 1980s and early 1990s. A Harvard political scientist, Daniel
Hopkins, has analysed 18 contests for the US Senate and state governorships
where black candidates stood and polls were published. He finds that until 1996
the polls overstated support for black candidates by an average of three
percentage points – but have not done so since then.
There are two possible reasons why things
have changed. The first is that the notion of black Americans holding elective
office is now more acceptable than it was. The second is that much of the
‘Bradley effect’ was linked to fears of crime, and the belief – conscious or
subconscious – that black Americans were more likely than white Americans to be
criminals. But since the early nineties, crime has been falling, especially in
the big American cities, and the issue is far less of a concern than it was.
Against this, proponents of the Bradley
effect point to the New Hampshire
primary nine months ago, when both the pre-election polls and exit poll
pointed, wrongly, to a clear Obama win. These polls can be explained in two
ways. The first is that the campaign polls failed to detect a late swing to
Hillary Clinton; the second is that there was a response bias in the exit
polls, with well-educated (mainly Obama-supporting) voters willingly giving
their views after they voted, while less well-educated (mainly
Clinton-supporting) voters not taking part. Like campaign polls, exit polls
correct for age and gender biases in response rates, as fieldworkers note the
gender and guess the age of non-respondents; but, unlike campaign polls, exit
polls DON’T correct for education (because it’s impossible to guess the level
of education achieved by non-respondents).
Besides, apart from New Hampshire, there’s no evidence that the
polls systematically overstated Obama’s support in the primaries. Indeed,
according to an analysis by the website pollster.com, the polls actually
UNDERSTATED Obama’s support in the primaries by an average of just over three
points.
Interestingly, there seems to have been a
regional pattern, with Obama’s support being systematically understated in
states with a large black population, including the key swing states of
Virginia and North Carolina, raising the suggestion that in some parts of
America there may be a ‘reverse Bradley effect’, with polls failing fully to
detect the enthusiasm for Obama among black Americans, especially younger
electors – people who have generally not bothered to register or vote at all.
This brings us to the arguments of those
who think Obama might win by a bigger margin than the polls currently indicate.
Because turnout in American elections has tended to be lower than in Europe,
polls need to screen respondents, and count only those who they think will
actually take the trouble to vote. It could be that the polls are screening out
too many young and black Americans. This is partly because Obama’s
well-resourced campaign has had some amazing successes with registration drives
in the key battleground states. (Around one in four adults who are entitled to
vote have traditionally not applied to join their state’s electoral register.)
It’s hard for polls to keep up with the most up-to-date registration data, and
some may be behind the curve in counting the proportion of pro-Obama voters in
the registered electorate.
In short, it is possible that the polls are
underestimating Obama’s support, especially in the battleground states, with
the result that Obama could win a comfortable majority of the national vote,
and a large majority in the electoral college vote.
And yet, and yet. All the evidence we have
from past polls relate to state-level contests, for the US senate, or state
governorships, of this year’s primaries. It’s possible that the polling
dynamics of a national election are different. Some (though by no means all) of
Obama’s supporters in the political science community remain edgy.
Personally, the poll I’ll be watching out
for is the final state-by-state surveys conducted by our US company,
YouGov-Polimetrix. They have already conducted two large-sample surveys for
CBS’s network news. Their final figures will be broadcast by CBS and posted on
the pollster.com website just before polling day. As online researchers with no
interviewers for respondents to talk to, they should not be as prone as
traditional telephone or face-to-face polls to any ‘Bradley effect’. And
YouGov-Polimetrix is seeking to apply the latest registration data to their
samples.
In just over two weeks we shall finally
know the result of the election, and may have a better idea of whether the
‘Bradley effect’ can finally be laid to rest."
Peter Kellner is the president of YouGov.
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