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who's going to win america's election
today was the day of a thousand polls
it's a question
everyone is trying to answer joe biden
up over president trump donald trump is
within the margin of
error most of the focus is on the
presidency
but there's another crucial race with
democrats and republicans battling for
control of the senate in 2020
the democrats hope this is their chance
to win back the senate
after five years the democrats are in
with a shot of taking back america's
senate
but with 35 individual races to follow
the result is harder to predict than the
presidency
so how do you work out who will win the
economist
might have the answer
control of congress can make or break a
presidency
especially one intent on delivering
change
if you just look at the presidency of
barack obama
he passed a bunch of major legislation
during the first two years of his term
the health care reform also the
financial reform and then once the
republicans
won the house in 2010 that was that no
more
legislative achievements for six years
mitch mcconnell the senate majority
leader at the end of barack obama's time
in office
saw blocking democratic motions as part
and parcel
of his job i was in charge of what we
did the last two years of the obama
administration i give you
full credit for that there is no doubt
in my mind that if joe biden wins the
presidency
mitch mcconnell will respond to his
nominees and legislative initiatives
exactly the way
he did to barack obama which is to block
everything that he possibly can
there are 35 senate seats up for grabs
in november
the republicans are defending 23 seats
the democrats 12. to take control
the democrats will need to gain at least
four three if biden wins the presidency
as the vice president decides on tied
votes
but trying to predict the result is not
an easy task
there's so many different races with so
many different candidates and so many
different polls i mean there's just no
way that
one person could keep track of it all in
their head and
fortunately we have computers to do that
for us
earlier this year dan began work on
creating a model to predict the result
of the senate vote
it was probably a good three months
of non-stop work including nights and
weekends
this july august september it's about as
big as
a project as anything i've ever done
all of that work for one crucial number
the percentage chance of a victory
as of october 6th our model gave the
democrats a 71
chance of winning the senate if you
click on the link above
it'll take you to the most up-to-date
forecasting
but why trust this number more than the
polls
the economist model takes in two sources
of information to produce its
predictions
the first is those polls
you can get quite accurate predictions
of
how legislative elections are going to
go using polls
when you have a lot of quality polls
taken really close to an election
the problem is the quality and quantity
of polls for senate races
vary widely state by state and every
race
counts that leaves you
very very in the dark in races that
don't have much or any polling
so the model also looks at a range of
historical factors
things like a state's voting history
whether a candidate is the incumbent
their political experience or how much
money they've raised
political science nerds call these
factors fundamentals
you can produce predictions of
results in these races based on all of
those
sort of benchmark quote-unquote
fundamental factors
without seeing a single poll but first
the model has to estimate the impact
each of those factors
is likely to have on the result to work
that out
it tests it on an election for which we
already know the result
you say okay let's give our model
the data from every election year except
for
say 1976. and based on everything we
knew from
every year but 1976 what would we have
predicted for 1976
it does terribly you say oops
that was over fit what were the least
useful variables in here the ones we
could most afford to do without and
let's get rid of them
and then even the really strong
variables let's maybe trim their effect
size by like 10
or something because you just never know
and you basically have the computer
just try a zillion of these permutations
until it finds the amount of shrinkage
that yields the best predictions on the
unseen dab
why go to all this trouble because
projections that combine polling data
with fundamental factors
tend to be much more stable than those
looking at polling alone
take the 1992 election where george h.w
bush lost the presidency to bill clinton
this
line marks his eventual share of the
vote
but in the months before the election
you'd have been hard-pressed to foresee
that
the polls were all over the place the
economist model would have been within
the margin of error throughout that
election year
so much for elections that have long
since been decided
what about the 2020 senate race
here's an example of how we rate the
chances that a republican senator
like susan collins from maine will
retain her seat
collins won the 2014 election for her
senate seat by a landslide
suggesting it's more likely she would be
voted in again
she also has the advantage of incumbency
something particularly important in
maine
but the democratic candidate sarah
gideon has raised more money in
fundraising
based on these and other fundamentals
the model had collins
eight points ahead but that's not the
end of the story
and then each time a poll comes in you
update
your prediction it will move
incrementally in the direction of
whatever the new pole you're adding says
there have been a number of high quality
poles in maine
the kind of pole our model weighs
heavily
with those factored in the forecast
swings in favor of her democratic
challenger
so which other races should you keep an
eye on
according to the economist model alabama
is very likely to switch from democrat
to republican
whilst arizona colorado and north
carolina
like maine have a good chance of
flipping the other way
if biden wins the presidency this map
would give the democrats their senate
majority
of course there's another challenge in
predicting the result of these
or any other race in the 2020 election
however good the model while in a
pandemic votes cast by mail are expected
to set a new record this november while
the experts say voting by mail is safe
it's yet another example of how it's
complicated
and it could be even more challenging
come november my
model does not make any
explicit adjustments for the fact that
this election
is occurring during the cobit pandemic
i think covet is a huge deal it's
obviously killed a huge amount of people
and of course it will cause changes in
the way we vote it could indeed have
significant unexpected you know
unmodelable effects
but
i'll need to see the evidence
without that evidence predicting how the
pandemic's going to affect this election
would call for forces far beyond science
i'm dan rosenhack the economist data
editor you can keep up to date on all of
our election coverage by clicking on the
link opposite
thank you for watching
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