election polls they're always wrong
aren't they you might as well get
monkeys to chuck darts at a board that's
not quite fair they're not completely
useless although you do have to be
careful how you interpret them so here
are some things to bear in mind about
how polls work first
you can't ask everyone more than 45
million people can vote at the next
election
you really can't talk to them all so
pollsters usually asked between 1,000
and 2,000 people a simple question if
there were general election tomorrow
which party would you vote for but if
you only asked pensioners or people in
Wales or the crowd at the Labour Party
conference
this wouldn't be representative but the
UK as a whole and you get a biased
result so polling companies try to build
a carefully balanced sample to get a
snapshot at the national news in just a
couple of thousand people but even with
a representative sample there are other
factors to consider for example older
people tend to be more likely to vote
than younger people and pollsters have
to factor this into their calculations
and turnout among different groups of
voters sort of the hardest things for
pollsters to predict accurately second
polls aren't perfect in the recent past
they've got it wrong because their
samples weren't quite right in 2015
pollsters counted too many labour
supporters and not enough of the people
who voted to keep David Cameron and
Downing Street but two years later the
polls were wrong the other way and
failed to pick up the scale of the
corbin surge there are often big
differences between pollsters and they
can't all be right so a bad sample
communal misses the mark but even with a
good sample polls cannot pinpoint a
party's exact vote share that's because
of something called the margin of error
when pollsters say that parties on 40%
what they really mean is they're
confident the party is somewhere between
36 percent and 44 percent so if a party
is up a bit in one poll this may not be
a genuine shift in the public mood third
despite all this polls often are quite
accurate for example they did a pretty
good job in recent European Parliament
elections
in the UK where polls have got it roll
but generally haven't been off by too
much we've had lots of close elections
recently and when a race is tight
a small polling myth can mean getting
the winner wrong fourth vote share
doesn't equal MPs the constituency based
voting system in the UK makes it
especially difficult to translate polls
on national party support into
parliamentary seats the Conservatives
gained votes in 2017 but lost seats
that's because it's not just about
whether a party does well overall but
about whether they do better than their
opponents in key constituencies ignore
anyone who has a simple formula to
predict he'll win the most seats so how
should you read the polls well keep in
mind and this is really important the
polls tell you about people's views a
specific point in time they're not a
prediction of the final result so if you
see a poll a few weeks away from an
election the final result may end up
very different not because the poll was
wrong but because people change their
minds also be very wary of any single
poll it's best to look at overall trends
from several different polling companies
our BBC poll tracker does this lastly
polls are interesting but don't obsess
over them too much as politicians like
to say the only poll that matters is the
one on election day