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发帖数: 804 | 1 https://news.usc.edu/109339/why-the-usc-dornsifel-a-times-presidential-poll-
is-unlike-other-polls/
The scientists behind the USC Dornsife/Los Angeles Times Presidential
Election Daybreak Poll have answered a list of frequently asked questions
about the national probability tracking poll that many media observers have
labeled as an “outlier” because its results have differed from other polls
’ since its July debut.
The results of the Daybreak Poll are updated nightly, and are publicly
available for downloading from the election.usc.edu website. The probability
poll is run in partnership with the Times and two USC research centers: the
Center for Economic and Social Research and the Jesse M. Unruh Institute
for Politics, both at the USC Dornsife College of Letters, Arts and Sciences.
The scientists behind the poll who responded jointly to these questions are
Unruh Institute Director and Professor of Political Science Dan Schnur, CESR
Director and Professor of Economics Arie Kapteyn and CESR Survey Director
Jill Darling.
What makes this a “probability” poll and is it unique?
The Daybreak Poll is a probability survey whose methodology aims to provide
a best estimate of how America plans to vote in the November election based
on the expressed intent of potential voters. The poll’s probability
approach seeks to measure participants’ level of certainty in their plans
to vote and the intensity of their commitment to a candidate, rather than
simply their preference for one candidate. The Daybreak Poll is one of only
a few such daily probability polls that exist in the country.
What questions are asked of participants?
Most surveys ask respondents whom they will vote for. The Daybreak Poll
instead asks eligible voters in the Understanding America Study election
panel every day online: What is the percent chance that:
You will vote in the presidential election?
You will vote for Hillary Clinton, Donald Trump or someone else?
Clinton, Trump or someone else will win?
Participants rate their chances of voting and the candidates’ chances of
winning on a 0 – 100 percent scale. In addition, to learn more about what
lies behind their likely vote, respondents each week are also asked one or
two extra questions about their preferences or values.
Is the poll weighted? Why?
Yes. To ensure representativeness, results are weighted on demographic
variables, such as gender, race and socioeconomic variables from the U.S.
Census Current Population Survey, as well as on how participants said they
voted in the 2012 presidential election. For example, the poll adjusts the
proportion of men and women to 48 percent and 52 percent, respectively.
Who are the poll’s participants?
More than 3,200 participants in the larger Understanding America Study are
on the election panel for the Daybreak Poll. Of those, one seventh — nearly
450 people — are invited daily to participate in the Daybreak Poll to
ensure a balanced sample. The participants are 18 and older, sampled to be
representative of all eligible voters across the United States.
What makes this a “tracking” poll?
The poll checks in once a week with the same group of people to measure
changes in their opinion up until they vote in November. Results are updated
nightly at midnight online. The results are based on a continuous, rolling
seven-day average.
Does the poll use a likely voter model?
No. However, more weight is given to voters who express a greater degree of
certainty that they will vote in November. Rather than assume that every
voter is equally sure of his or her allegiance to one candidate or the other
and is just as certain to vote, the Daybreak Poll asks participants to rate
their likelihood of voting and voting for each candidate. To estimate the
vote, we calculate the ratio of a participant’s likelihood of voting to his
or her likelihood to vote for a candidate.
Sometimes the Daybreak Poll results do not resemble other poll results. Why?
Like any other election poll, the Daybreak Poll is designed to estimate the
presidential election outcome. It uses an innovative approach that makes it
difficult to compare the results with other polls’ results.
Some of these differences include:
Our questions allow voters to express a greater level of uncertainty than
traditional poll questions which force respondents to choose a single
candidate or say that they “don’t know.” For example, in the Daybreak
Poll, a respondent might say that they are 60 percent for Clinton and 40
percent for Trump.
We include voters who did not vote in the prior presidential election and
others who may be considered “less likely to vote.” Many traditional polls
exclude some or all of these voters. We weight our results based on turnout
in the 2012 election to account for differential response rates. We used
this approach very successfully to predict the 2012 election outcome. Our
final prediction was a 3.32 points advantage for Obama. The final tally of
the popular vote showed a 3.85 points advantage. Our prediction was at least
a couple of points more in Obama’s favor than most of the other tracking
polls.
The panel of respondents answer the survey questions once a week, versus
traditional polls that collect data periodically.
Our poll is internet-based. Studies have indicated that people are sometimes
more honest about their voting preferences when completing internet surveys
than they are in phone surveys.
We randomly recruit participants from households nationwide, providing
internet service and an internet-connected tablet computer to those who do
not already have it. Therefore, our sample includes a proportion of
individuals who cannot be represented in web-based polls that do not provide
such access.
Our participants can answer poll questions at any time of the day or night.
We give them seven days to do it; thus, our sample is likely to include more
voters who are difficult to reach by phone during traditional telephone
polling hours.
Why are there temporary “bumps” in candidate support in the subgroup
charts? Why do the gray bars increase?
The Daybreak Poll uses a complex weighting scheme to ensure results are as
representative of the population as possible. Therefore, underrepresented
groups are assigned a greater weight than overrepresented groups. If members
of an underrepresented group change their voting intention or vote
intensity, this may have a larger effect on results than when other
respondents change their preference. In the charts, we take this added
variability into account. An example can be seen in our African-American
voter chart. If respondents assigned higher weights “vote,” the chart may
show a bump or a dip while the width of the confidence interval — the gray
zone between the red and blue lines — increases.
It is important to note that some of the subgroups that we chart have a
modest number of observations. Due to this limitation, we advise against
overinterpreting day-to-day changes. The inclusion of a small number of
individuals within a group may appear to have sizable effects, but the
overall prediction of the popular vote’s outcome is much less affected.
Indeed, the confidence interval for the overall prediction is much smaller
but wide enough that we cannot confidently say who will win the popular vote
. For more information on weighting in the Daybreak Poll, consult our
detailed methods document.
Is the Daybreak Poll more accurate than other polls?
Four years ago, the team responsible for the Daybreak Poll had developed the
successful RAND Continuous Presidential Election Poll based on the same
methodology, with very successful results. We believe that our sample this
year is a reliable representation of the U.S. eligible voter population, and
that our methods are based on sound science. Is our approach more or less
reliable and accurate than other polls? Only time will tell.
Why are you doing this?
The Daybreak Poll is part of an ongoing experiment to study whether the
methods we have helped pioneer are useful in increasing the accuracy of
election polling. To this end, we practice full transparency. We publish our
findings on a daily basis, provide full public access to our data even as
the election is underway, and we publish detailed documents that allow other
scientists to reproduce our model or create their own in real time or later
once election results are known. Other investigators have added questions
to the poll that allow them to study election behavior. Their findings may
also contribute to the accuracy of election polling.
What if the poll turns out to be wrong?
Public opinion polling is not an exact science, but through research it
could become more so. Whether or not our poll results closely reflect the
election outcome, we will review our methodology and improve it for the next
election, sharing our findings and our data with other researchers. One of
the areas of intense interest for us is in comparison of self-reported vote
to actual vote, and we will follow up this poll with analysis in that area,
among others. | m*******p
发帖数: 1978 | 2 这里的几个床粉基本是文盲，不会花时间读大段英文的。
有兴趣的可以去读读 NYTimes的文章讨论这个USC/LA Times poll为什么这么奇怪。 |
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