[MUSIC PLAYING]
SAM WANG: It's common these days for voters to feel frustrated.
To feel as if legislators aren't paying attention
to them, whether it's the Flint water crisis in Michigan
or partisan polarization or other ways in which legislators
seem to not heed their constituents’ opinions.
Legislative seats nationwide are less competitive
than they used to be.
And one big reason why is gerrymandering.
Voters have chosen to arrange themselves
in cities and towns in rural areas,
and then legislators take that natural pattern
and draw the lines as they like to suit themselves.
A major problem is partisan gerrymandering,
drawing a whole pattern of districts to suit
one whole political party.
Redistricting happens every 10 years.
This leads to a situation in which
close to 100 seats in Congress are less competitive than they
would be otherwise.
Intuitively we think about gerrymandering
as centering around weird shaped boundaries, right?
Strangely shaped boundaries that are
crooked that have funny bumps and valleys and so on.
It turns out that's not such a great way
to define a gerrymander.
Because voters tend to live in communities of like mindedness,
imagine a city that is mostly Democrats
and imagine it surrounded by a community of voters
who are mostly Republicans distributed over space.
It is possible to creatively draw lines
where we can pack the Democrats in one district,
for instance, by drawing a boundary
that encompasses most of the Democrats
in a single nicely circularly shaped district,
and then distributing the remaining Democrats
over remaining districts so that in the end
the Republicans get an overwhelming advantage.
You can take the same map and do the opposite.
You can take this nice cluster of voters in the center
and now take wedges out of that center city
and now create pie slices, and the first bite of each pizza
slice will then be just enough to make that slice
a secure win for Democrats.
Therefore it's possible to draw lines
to make it either running the table for Republicans
or running the table for Democrats,
depending on what legislators want.
So what's left is to come up with some standard
where gerrymandering can be defined
without reference to maps.
And it turns out there is a tool available.
The idea is to invoke the idea of partisan symmetry.
If one side has 75, 80 percent of the vote in district
after district, that side has been packed.
When one side wins in landslides,
but the other side's wins are closer,
the question arises, did this overall pattern
occur incidentally as if by chance or by nonpartisan means?
If not, then we would conclude that one side's voters
were packed more than the others as if on purpose.
It turns out this is the easiest thing that you can test.
In all the sciences and all of engineering,
the most widely used test is something
called Student's T-test.
And it was made possible by this guy William Gosset.
Gosset lived in the early 20th century.
He was chief experimental brewer of the Guinness Company
in Ireland.
Gosset had this problem of how to tell if whether hops quality
was good.
And he was very pleased about this.
And he said OK, I would like to publish this.
And his lab notebook said student’s laboratory notebook.
And he had a bit of a sense of humor,
and he said, oh I'm a student.
And so to this day it's called Student's T-test.
The T-test compares two averages.
Here the two averages are of the winning vote
share in Democratic districts and the winning vote
share in Republican districts.
The T-test asks whether two averages are different enough
that they are unlikely to have arisen incidentally
from nonpartisan mechanisms.
For example, redistricters want to draw
straight-ish boundaries.
They want to honor communities of interest.
They want to follow other rules that are set down in law.
And for those reasons, averages can sometimes
be a little bit different, advantaging
one side or the other side.
What the T-test asks is, is that difference so large
that it could not have arisen incidentally?
And if that's the case, then what we have
is a likely gerrymander.
A great example of partisan asymmetry
that can be detected using the T-test is North Carolina.
2010 was a wave election for the Republicans.
And with their new control over the redistricting process,
they created an advantage for themselves.
It was a perfect inversion of what had happened previously.
Democrats ended up with four congressional districts
and Republicans ended up with nine congressional districts,
despite the fact that Democratic candidates won
more votes that year.
This pattern was repeated in 2014 and 2016.
And in each case, the vote was reasonably closely split,
but in each case, the Democrats won more lopsided wins.
And the T-test tells us that this difference
between Democratic wins and Republican wins
could not have arisen by chance.
There is overwhelming public opinion
against gerrymandering and a general sense
that it ought to be addressed.
And there are two ways.
One is through courts and the other is by activists.
Courts could say we will define gerrymandering as violation
of partisan symmetry.
Are the two parties being treated fairly and equally?
And if they're not, then there's partisan asymmetry.
And the Supreme Court has expressed some willingness
to do that.
Another route is for activists.
Voters have started to pass fair districting laws.
The risk is that they may leave loopholes
by not thinking ahead and realizing that in fact there
is still the possibility of partisan asymmetry,
so writing into the law something
like a simple statistical test like the T-test would
close that last loophole.
Here's an opportunity to make the democratic process
work a little bit better.
If this effort succeeds, what we're going to end up with
is a situation that the founders envisioned.
The voters pick their legislators and not
the other way around.