Democrats won the popular vote for Congress, but Republicans maintained a majority

Posted by AzBlueMeanie:

John Sides at The Monkey Cage reports this analysis by Nicholas Goedert, a Postdoctoral Fellow at Washington university, on the question of why Democrats won the popular vote for Congress, but Republicans maintained their majority. Not Gerrymandering, but Districting: More Evidence on How Democrats Won the Popular Vote but Lost the Congress:

This is a guest post by political scientist Nicholas Goedert, who is a Postdoctoral Fellow at Washington University.

*****

Expanding on recent posts by Dan Hopkins and Eric McGhee,
there appears to be evidence at a state-by-state level that the
disparity between the popular vote in the House and the distribution of
seats is not just due to Republican gerrymanders, but due to a skewed
geographic distribution of population putting the Democrats at an
inherent disadvantage
, along the lines of Chen and Rodden’s recent work. That is, the Democrats’ loss in the House was caused largely not by gerrymandering, but districting itself.

McGhee’s post compares the results of the 2012 elections to what the
election might have looked like using the 2002-2010 maps, and finds that
the most recent round of redistricting had relatively minimal
effects. An alternate way of measure districting effects is to compare
the 2012 results with historical patterns from recent congressional
elections for seats won for a given popular vote share.  Using
this technique, I find slightly greater effects of partisan
gerrymandering, but also a persistent bias in favor of the Republicans.

* * *

In every state districted by Republicans, Democrats won fewer seats
than their historical expectation, and in six cases they underperformed
by 20% or more (as a percentage of total seats up for election). So it appears that Republicans gained benefits across the board from controlling the redistricting process.

By contrast, Democrats exceeded their expected seat share only slightly in the three states where they controlled the process . . . Democrats gained just a fractional seat above expectation in each such
state. For instance, Illinois Democrats won a smaller majority in their
delegation than Pennsylvania or Ohio Republicans won in theirs, despite
winning a much larger vote share.

* * *

But partisan control of redistricting cannot completely explain each
party’s performance relative to the hypothetical unbiased map.  Instead,
we still observe bias even where we should expect none in the
redistricting process . . . Democrats also fell
short in several states with bipartisan or court-drawn maps, winning on
average 7% fewer seats than expected.

* * *

So how many seats did this underlying disadvantage cost the Democrats? 
If we were to imagine that these bipartisan or court maps were unbiased,
and Democrats received the same benefit from their own maps that
Republicans received from theirs (let’s say a 13% advantage as an
average), this would have yielded 14 additional seats, likely getting the Democrats within 3 or 4 seats of the majority.

If there is any area of the country where the geographic distribution of partisans has not led
to an underrepresentation of, we might expect to observe it where
Democratic voting strength does not hue as closely to the black/white or
urban/rural divide.  In particular, we find this pattern interrupted in areas with very strong Hispanic populations . . . [Arizona, California and Texas]  three large states with the highest proportion of Hispanics, revealing
that Democrats won a seat share very similar to their expected share in
each of these states, despite not controlling the process in any of
them.  It is possible that nonpartisan commissions [Arizona, California] may have contributed
to greater fairness
, but the ease of drawing geographically large,
majority Hispanic districts in these states, (e.g. AZ-2, CA-16, CA-51,
and TX-23) might have also mitigated the natural advantage Republicans
have in other regions in the distribution of the their vote.

* * *

In direct support of the Chen and Rodden argument, states that
are heavily urbanized (such as New Jersey and Pennsylvania) are more
distorted against Democrats than more rural states (such as Minnesota
and Wisconsin).
Indeed, urbanization has a negative and
significant effect on the difference between seats won by Democrats and
expected seats
, even after controlling for the party in control of
redistricting.

Of course, this analysis does not imply that Democrats are doomed to the
minority for the foreseeable future, or even the next decade . . . But because of unequal concentrations of vote share in most states,
not just those with Republican gerrymanders, a Democratic majority will
be more difficult than it should be. And this difficulty persists even
when both parties agree to the maps.

Changing our redistricting institutions alone will not assure national proportionality.

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