The Pseudo-Paradox of Partisan Mapmaking and Congressional Competition

Nicholas Goedert Washington University in St. Louis

November 2013

ABSTRACT: This paper uses empirical evidence from four decades of congressional elections to examine how redistricting institutions influence congressional seat competition under changing partisan tides. In particular, the paper finds that partisan gerrymanders induce greater competitiveness as national tides increases, largely due to unanticipated consequences of waves adverse to the map-drawing party. These results explain the “pseudo-paradox” that less competition in the national congressional popular vote historically predicts greater competition in individual local races. In contrast, bipartisan maps are shown to induce lower competition, and nonpartisan maps higher competition, under all electoral conditions and competitiveness measures.

Word Count: 6678 (all-inclusive); 5197 (body text only)

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The link between electoral competition and accountability has been a focus of both public

and academic debate since the founding of democracy. In the United States in recent years,

much of this debate has targeted congressional elections, with good-government groups and the

media worrying about the overwhelming number of seemingly entrenched incumbents, and

scholars of American politics trying to explain why the number of close elections seemed to be

low and declining. This paper addresses one common explanation for declining competition,

gerrymandering, but with a less common focus: maps drawn for partisan advantage, specifically

in interaction with national partisan tides. We find that partisan gerrymandering explains both

variation in congressional competition, and the perverse connection between national partisan

balance and the prevalence of close elections at the district level.

Much of this concern about noncompetitive elections and entrenched incumbency has

highlighted the recent period in the late 1990’s and early 2000’s when competition appears

historically low. But this period was immediately followed by three consecutive elections from

2006 to 2010 where a significant number of incumbents were defeated, and the make-up of the

U.S. Congress changed dramatically. And it does not seem like the research has caught up with

this era, either by arguing that these elections were a fluke, or that the overall pattern of reduced

competition has now been reversed.

This paper argues that partisan gerrymandering has had a profound effect on

congressional competition, both during times of close partisan balance and times when one party

is ascendant, but that this effect can only be observed in interaction with these short-term

national electoral trends. Specifically, we find evidence that trends in the competitiveness of

congressional races have been largely driven by “backlash” responses of partisan gerrymanders

to national wave elections. This pattern among partisan maps also generates a somewhat

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paradoxical inverse relationship between national and district competition, where greater parity

between parties at the national level correlates with reduced competition at the local level in

congressional campaigns. While the electoral effects of bipartisan gerrymanders and nonpartisan

commission maps tend to be resilient to tides (with nonpartisan maps generating consistently

more close races than bipartisan ones), partisan maps suppress competition when the national

electoral environment is closely balanced, but incite it when one party wins a substantial national

majority, largely due to members of the map-drawing party facing unexpectedly close races.

The argument of the paper proceeds as follows. First, in accordance with conventional

wisdom and past research, we show that both bipartisan and partisan-controlled legislatures draw

fewer competitive districts than nonpartisan commissions. However, we next show that a

previously unacknowledged factor, national tides, strongly and negatively correlates with

competitive elections. Finally, we demonstrate how this interaction of national and district-level

competitiveness is explained by focusing on partisan gerrymanders. Specifically, partisan

gerrymanders increase close elections during wave cycles because of unanticipated competition

in states with maps drawn by a party suffering through adverse tides. This argument is advanced

through an analysis of various measures of competition in a data set encompassing the past forty

years of congressional elections.

Previous Research on Districting and Competition

Declining competition in U.S. congressional elections has worried scholars since David

Mayhew’s seminal article “The Case of the Vanishing Marginals” (1974). Mayhew does not

arrive at an explanation for the paucity of close elections and districts that he observes, but the

role of redistricting in fostering or suppressing such competition has been controversial

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throughout subsequent work. Tufte (1973) argues that redistricting was the cause for a reduction

in marginal seats during the 1960’s. However, later studies concluded that redistricting, whether

partisan or bipartisan, has had little effect on the competitiveness of seats or the advantages of

incumbency (Glazer et al. 1987, Ferejohn 1977). Moreover, Gelman and King (1994) find that

temporally proximate redistricting, both partisan and bipartisan, leads to an increase in electoral

responsiveness in state elections, measured by the slope of the seats/votes curve. And Gopoian

and West (1984) suggest that many partisan maps in the 1980’s appear to have reduced the

security of their incumbents, from an analysis of vote margins in two electoral cycles.

Scholars took up this topic in perhaps the greatest force in the mid-2000’s, when

competitive elections were are their lowest ebb. Most commonly, research points to bipartisan

legislative agreements as reducing competition and nonpartisan commissions as encouraging it.

Carson and Crespin (2004) find evidence that courts and commissions increase competition in

years immediately following redistricting (using data from 1992 and 2002). Lindgren and

Southwell (2013) also argue that independent commissions did reduce average margin of victory

in U.S. house elections from 2002-2010. But neither of these articles distinguishes between

bipartisan and partisan legislative maps. More generally, Cain et al. (2005) find that an overall

decline in competitive elections has tracked with an increase in the number of districts drawn by

bipartisan agreement.

Yet other recent works claim much less of a role for districting in contributing to this

trend. In an examination of state legislative elections in 2000 to 2008 (and using the same

definition of competitive elections as this paper), Masket et al. (2012) find little impact of

redistricting institutions on the likelihood of a close election. And Abramowitz et al. (2006) find

that while much of the decline in competition since the 1970’s can be attributed to the increased

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partisan polarization of districts, this is explained much more by population sorting than

intentional districting.

And the specific role of partisan districting is inducing or suppressing competition is

perhaps even more ambiguous. Hirsch (2003) focuses on Republican-drawn maps as causing

historically low competiveness in the 2002 elections. But employing data from the same election

cycle, Yoshinaka and Murphy (2011) find that partisan maps increase competition specifically in

years immediately following redistricting, but constrain their explanation to the deliberately

increased difficulty that out-party members face, rather than unanticipated close races faced by

in-party members in the face of unexpected waves.

Yet the fact that partisan gerrymanders do not always turn out as planned for the

controlling party has not gone unnoticed by scholars. Grofman and Brunell (2005), in a series of

short case studies referred to as “dummymanders”, show that many maps drawn by Southern

Democrats in the 1990’s failed to anticipate trends favoring the Republican party. Conversely,

Seabrook (2010) argues that the effects of Republican partisan maps were largely washed out by

mid-decade partisan trends in the 2000’s. However, the larger effect of “dummymanders” on

competition, and the frequency of the their occurrence, is largely yet unexamined beyond

anecdotal evidence and narrow case studies.

Why Partisan Gerrymanders?

It is easy to see why scholars have focused on contrasting bipartisan and nonpartisan

maps in their study of gerrymandering and competition; the incentives and constraints of these

institutions make it obvious what the hypothesized effect on competition should be. In the case

of commissions, it is sometimes true that the creation of balanced districts is a stated goal of

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nonpartisan actors: the Arizona Proposition creating that state’s districting commission requires

“competitive districts are to be favored” as long as they comply with other constitutional

requirements (Adams 2005, Kang 2004). In other cases, it is a side effect of other provisions: the

Legislative Services Bureau responsible for districting in Iowa is not permitted to incorporate

incumbency or voting data in creating their proposals. On the flip side, without the added

incentive of maximizing one party’s seats, the uniform desire to protect incumbents of both

parties in the case of bipartisan maps leads in many cases to districts clearly drawn to be

noncompetitive. Figure 1 below acutely exemplifies this in the case of the 2002 California map.

But the expected effect of partisan maps on competition is less obvious; the desires of a

party to maximize seats and simultaneously protect their own incumbents work at cross-

purposes, and it is up to the individual map-maker to choose how much emphasis to place on

each goal. Cain (1985) shows how partisan mapmakers “packed and cracked” opposing party

members into a small number of safe districts, and this has become the standard strategy for

partisan gerrymanders. Yet, a broad array of tactics are available within this strategy. If too

many opposing districts are “cracked”, mapmakers risk spreading their own party’s voters too

thin, leaving many of their own incumbents at risk if political tides shift slightly against them.

But if partisans fortify all their own districts safely enough to withstand an unlikely adverse

wave, they fail to contest seats that could have been won under more typical electoral

environments. Additionally, Niemi and Deegan (1978) demonstrate formally how neutrality and

competitiveness may be at odds when the overall vote is not evenly split, even when a fair map is

desired.

The range of “aggressiveness” (i.e. willingness to risk their own party’s seats to

maximize expected seats) that partisan mapmakers chose in the 2000’s is also shown in Figure 1

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below, which gives a visual representation of three Republican-controlled gerrymanders

(Pennsylvania, Ohio and Florida) and one bipartisan gerrymander (California) used in the 2002

elections. The x-axis in these density plot figures represents how heavily-Republican a

congressional district is (measured by Cook PVI), while the y-axis represents the share of

congressional districts in each state with that level of partisanship (PVI’s more extreme than 20

or -20 are coded as 20 and -20 respectively).

We immediately see the stark difference between the partisan maps and the bipartisan

one. The three Republican maps have a clear slightly pro-Republican peak, accompanied by

several extremely safe Democratic districts (usually majority African-American). In contrast,

California has no districts in the middle of the graph (indicating districts that would be

competitive at the presidential level), and a clear bimodal distribution of both strongly

Republican and strongly Democratic districts. In this map, we would expect very few

competitive elections unless tides in favor of one party or the other were almost historically

extremely.

[Figure 1 about here]

But although each Republican map seems to have more districts on the positive (pro-

Republican) side of 0, the aggressiveness of each map, and thus their propensity to withstand

changes in political climate, varies. In Pennsylvania, the bulk of congressional districts lie

between D+2 and R+4; Republicans in Pennsylvania drew several swing districts that they were

counting on factors like incumbency and continued close national elections to hold. Ohio, with

its peak around R+2, was also very aggressive, but slightly less so than Pennsylvania. Florida,

with a peak around R+5, is a more moderate gerrymander, with many districts reinforced from

mild swings toward the Democratic party. The differences between these partisan maps help

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explain why Republicans lost 9 of their 24 seats in Pennsylvania and Ohio in the 2006 and 2008

elections, but only 3 of 18 seats in Florida.

This paper hypothesizes that a typical strategy employed by partisan mapmakers,

exemplified above, will be to draw seats that will be largely safe for their own incumbents under

neutral electoral conditions (when the national popular vote is closely contested), but which will

become increasingly competitive as national tides adverse to the gerrymandering party increase.

Thus, the overall effect of partisan gerrymanders on competition can only be considered in

interaction with national competition.

Hypotheses

From past research on bipartisan and nonpartisan gerrymander, and anecdotal evidence on

partisan maps and occasional resulting “dummymaders” we would expect to see the following

interactions between national tides and redistricting institutions:1

• We expect low competitiveness in districts drawn by bipartisan agreement regardless of

electoral environment.

• We expect high competitiveness among districts drawn by nonpartisan commissions

when the national electoral environment is close. As national tides increase,

competitiveness in these districts may decline or stay steady.2

• When the national electoral environment is close, we expect low competitiveness among

districts drawn by legislatures controlled by one party. As national tides increase, we

expect competitiveness to increase, particularly when tides run adverse to the

gerrymandering party.

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Measures & Controls

For the purpose of testing these predictions on competitiveness and partisan bias, we have

assembled a data set of all congressional elections falling on a national election day from 1972

(following the first national round of post-Wesberry redistricting) through 2010. The process by

which each state was redistricted at the start of the decade was coded as Democratic-controlled,

Republican-controlled, bipartisan, nonpartisan commission, or court.3 States with three or fewer

congressional districts are designated as “small states” and not otherwise coded. It is less feasible

to draw maps to serve partisan interests, or achieve other very particular goals, in states with very

few districts, particularly those with only one. Therefore, these small states, will serve as

controls against which to measure the effects of the regimes of interest. Maps drawn by courts

serve as a separate control for which we provide no particular directional predictions.4

This analysis attempts to isolate the effects of the redistricting institution and not the

effects of the specific districts drawn. Therefore, any controls that might be endogenous to the

actual districts have been deliberately omitted (with the exception of denoting open seats in one

specification for illustrative purposes). This of course includes district-specific demographics

and partisanship, but also candidate-specific data like campaign spending and incumbency.

Although all of these factors are of course important to the outcome of a congressional race, the

controls that are included (statewide presidential vote, region and statewide demographics, and

redistricting institution) are causally prior, and thus the exclusion of district-specific factors

should not contaminate the coefficients testing the theory.5 Errors are clustered by district

interacted with decade to account for serial autocorrelation within districts.

To get a complete picture of the effects of redistricting on competition, we employ four

measures of competitiveness: the competitiveness of (1) the state as a whole; (2) the

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congressional district’s relative to the nation; (3) the national electorate in an individual election

year; and (4) the individual congressional race in a specific year and district.

The first of these measures is Statewide Competition, a measure of the competitiveness of

the state, with lower values indicating swing states and higher values indicating ideologically

extreme states. It is the absolute value Statewide Presidential Vote, defined the difference

between the average statewide GOP presidential vote margin and the average national GOP vote

margin over the previous two elections for a given district in a given year. Thus, Statewide

Presidential Vote is a rough measure of a state’s ideology in a given election cycle. E.g. for the

California 1st district in 2006, this variable takes a value of -13, because California voted 13%

more Democratic than the nation in the 2000 and 2004 presidential elections.

The second measure, District Level Presidential Competition, is the amount by which

presidential results in each district deviate from the national average. It is the analogous to

Statewide Competition (though scaled the same as Cook’s PVI), for the individual congressional

district, with lower values indicating swing districts at the national level. It is used as a

dependent variable in the next section.

The third competitiveness measure is National Tides, derived from National GOP Vote

Margin, the GOP margin in the nationwide congressional popular vote in a given cycle. For

example, the variable takes a value of -7.9 for all 2006 data points, because Democrats won the

national congressional popular vote that year by 7.9%. National Tides, the magnitude of tides

without regard to their direction, is the absolute value of National GOP Vote Margin, with

greater values indicating a stronger wave. Note that in our data set, eleven of the 20 elections in

the data set saw a national popular vote advantage for the Democrats of greater than 5%, only

two elections saw so great a national advantage for Republicans (1994 and 2010). So our ability

10

to test our predictions with respect to the interaction of Republican waves on Democratic

gerrymanders will largely be limited to the anecdotal.

The final measure, Close Race, is a dummy variable coded as 1 if an individual

congressional election was won by less than 10 points.6 As we are mainly interested in how

often congressional elections are competitive, this is the dependent variable throughout most of

the analysis. Overall, 14% of congressional elections are Close Races under this definition.

Demographic Competitiveness

In response to the scholarship on the competition created by legislative versus non-

partisan drawn maps, we might first ask whether gerrymandering institutions influence the

inherent partisan balance of districts, independent of waves in individual election cycles. To do

this, we regress District Level Presidential Competition, for all districts immediately following a

national districting year from the 1970’s through the 2000’s, on various gerrymandering controls.

We also include a control for the overall partisanship of the state, Statewide Competition, since

this might influence both the districting institution and the resultant districts. Lower values for

both “competition” variables indicate a swing state or swing district.

The results of this analysis are shown below in Table 1. The first column isolates

nonpartisan institutions only, and its coefficient is negative and significant, indicating that

nonpartisan maps indeed tend to draw more swing districts. Additionally, the positive

coefficient for Statewide Competition indicates that districts with closer partisan balance tend to

occur more in swing states. But controlling for state-level partisanship, nonpartisan commissions

do also draw more balanced districts. The second column also includes controls for Democratic,

Republican, bipartisan, and court-drawn maps (with small states as the excluded category).

Under this specification, Republican, bipartisan, and court-drawn maps all create fewer swing

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districts that the control or nonpartisan maps; curiously, Democratic maps show no difference

from the control. However, this is likely an artifact of the global trends in the South during the

first half of this period, during which the region tended to vote consistently more Republican at

the presidential level than the congressional level, and had almost universally Democratic state

legislatures. This allowed Southern Democrats to draw many districts that would appear very

competitive when looking at presidential vote (how Statewide Competition is measured), but

were de facto safe Democratic seats at the congressional level. We can see that when the South

is excluded from the analysis in column 3 of Table 1, Democratic maps appear to draw just as

few swing districts as Republican and bipartisan maps.7 From this perspective, the tendency of

past literature to group partisan and nonpartisan gerrymanders together seems appropriate, and

that both do indeed produce fewer competitive districts. Conversely, the reforms intended to

produce more competitive districts under nonpartisan regimes, such as the commission in

Arizona or the bureaucracy in Iowa, have succeeded.

[Table 1 about here]

The Pseudoparadox of Competition

As discussed above, many of the recent claims about declining congressional

competition, in both the media and the literature, occurred in the wake of an era of parity at the

national level. Between 1996 and 2004, no party won a majority of the national popular vote in

congressional elections, nor did any party win that popular vote by more than 5 points, or win

more than 54% of congressional seats. This is actually something of a historical anomaly. Of

the twenty election cycles from 1972 to 2010, one party failed to win by at least 5-points in the

popular vote only seven times, included these five consecutive years. And during a time when

the country appeared so evenly divided, it would be intuitive to expect that many individual races

12

would also be close, but less than 11% of races during this era were decided by 10 points or less

(our definition of Close Races).

But this era of parity was immediately followed by three consecutive “wave” elections

from 2006 through 2010. And despite the national electorate clearly favoring one party in these

three years, the number of race that were closely contested rose to 15%. Recently, it does not

seem that close national competition has lead to greater competitiveness at the local level, and

this phenomenon is born out looking further into the past; this trend extends back at least as long

as the equal-population standard has been applied to congressional districts. Figure 2 below

shows the correlation of the proportions of Close Races in each cycle 1972-2010 with National

Tides; as the national popular vote gets closer, the number of competitive races tends to decline.

[Figure 2 about here]

As a more rigorous test, Table 2 below shows the effect of National Tides on the

percentage of Close Races (each data point is an individual race, with races clustered by state

crossed with decade) from 1972-2010, when we control for the competitiveness of individual

states by including Statewide Competition. In the first column, we see that the competiveness of

a state has very little effect on its propensity toward competitive congressional elections.8

However, the positive coefficient on National Tides (significant at p<.01), indicates that extreme

wave elections do tend to create more close races. The second column excludes races in the

South, with no effect on the National Tides coefficient, indicating the phenomenon cannot

merely be explained by increased competitiveness of the Republican party in the South in the

most recent decades, or the creation of majority-minority districts in those states. The third

column addresses the argument that competition has steadily declined over time, by including a

Year variable, as well as the argument that competition increases in years immediately following

13

redistricting (e.g. Yoshinaka and Murphy (2011); Hetherington et al. (2003)); the Gerrymander

Year dummy variable takes a value of 1 for election years ending in “2”. The coefficients for

these variables are slightly in the expected direction, but neither is significant, and neither

mediates the effect of National Tides on the number of close elections. Finally, we see in the

Figure 2 that 1974 appears to be an outlier both in terms of wave strength and number of close

races. The fourth column of Table 2 shows that the effect of National Tides on Close Races is

still significant at p<.05 even when this cycles is excluded.9

[Table 2 about here] Effects of Gerrymandering

So what explains this “pseudo-paradox” that less national competitiveness correlates with

greater local competition in congressional races? Figure 3 below shows that, far from being a

universal phenomenon, the pseudo-paradox appears limited only to states with partisan

gerrymanders. When we isolate only the partisan maps, the negative effect of national

competitiveness on local competitiveness is strengthened (and significant at p<.02). But the

magnitude of National Tides has no effect on competitive elections under bipartisan maps, which

follows if these maps drew districts safe enough for both parties to withstand strong tides in

either direction. Moreover, the coefficient for the nonpartisan maps is in the opposite direction

of partisan maps, although not significant due to the high variance from the small sample size;

this would also follow if such maps tended to draw many “naturally” competitive districts.

[Figure 3 about here]

Yet it is also possible that these observed differences are merely the result of the types of

states that tend to adopt these varying institutions. I.e perhaps swing states tend to adopt

nonpartisan regimes or extreme states adopt bipartisan regimes. So we also run a probit analysis

14

of Close Race on National Tides and the various gerrymander dummies including the Statewide

Competition control. We also assess the slope of the effect of tides by interacting National Tides

with the gerrymander dummies. As before, the unit of analysis in the first four columns Table 3

below is individual congressional races from 1972-2010, clustered by year crossed with decade.

The last two columns employ OLS on units of statewide means as described in Footnote 5, with

very similar results.

[Table 3 about here]

The first specification does not include any controls for redistricting institutions. For the

second and third specifications, the excluded category is the small states. The third specification

includes a dummy variable for whether an election was an open seat; although this is potentially

endogenous to the gerrymander, we include it merely to show that the results remain the same

with its inclusion, and thus retirements do not explain the results with respect to other variables.

Open seats do drastically increase competition (34% of open seat races are close, compared to

11% of races including an incumbent), but do not wipe out the effects of national tides or the

differences between redistricting regimes. Figure 4 below shows the probit coefficients for the

redistricting variables interpreted for neutral state and national electoral conditions.

[Figure 4 about here]

From the coefficients in all specifications, we see that bipartisan maps and partisan maps (from

both parties) create fewer close elections than elections in small states (the excluded category),

when controlling for state ideology and national tides. Conversely, nonpartisan commission

maps create more competitive elections, with an effect size large enough to be significant despite

the small sample size. From the figure, this analysis estimates that while only 8%-11% of

elections will be close races under neutral electoral conditions under partisan and bipartisan

15

maps, 21% of races will be close under nonpartisan commission maps.

Note that in all these specifications, the effect of National Tides is positive and

significant. We can test how this effect varies under different gerrymanders in two ways. First,

we can include interaction terms nested into the model run on the entire data set. This is shown

in column 4 of Table 3, which adds the interactions of each regime with tides. Consistent with

Figure 3, we see that the “pseudo-paradox” effect of tides is again largely explained by

gerrymandering institutions. When applied to bipartisan and nonpartisan gerrymanders, the

effect of National Tides is not significant, but it is still positive and significant when applied to

Democratic and Republican-drawn maps.10

As second way of analyzing this interacted effect would be to measure the effect of tides

on the data subsetted by redistricting regime. Table 4 shows the slope coefficient for the National

Tides variable when the probit from the first column of Table 3 is run only on subsets of districts

drawn under a particular institution. Again, the results conform to our predictions. We see a

large positive coefficient Republican partisan gerrymanders, (and a smaller, yet still significant,

one for Democratic maps) suggesting that partisans draw maps to protect their own seats

assuming a neutral environment, but suffer a backlash when tides go against them, leading to

many close races as national tides increase. In contrast, bipartisan gerrymanders, with safe

districts are drawn so as to be resilient to partisan tides, show no significant effect of tides, while

nonpartisan commissions show a negative but insignificant coefficient due to small sample size.

The difference between these coefficients for partisan and bipartisan maps is significant at p<.02.

In support of our hypotheses, competition at the district level increases as tides increase under

partisan maps, but not bipartisan or nonpartisan maps, controlling for statewide partisanship.

[Table 4 about here]

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Differences by Party

The results above suggests that partisan maps induce greater competition as national waves

increase, but the tell us nothing about the direction of that wave. Yet we hypothesize that we

should only observe greater competition under waves adverse to the map drawing party (i.e.

Republican maps under Democratic waves such as 1974 and 2008, and Democratic maps under

Republican waves like 1994). And specifically, we would hypothesize that the slope of the

National Tides coefficient for the subset of Democratic-drawn maps would be greater when

Republicans with the national popular vote than when Democrats win (and conversely for

Republican maps). Table 5 below confirms this hypothesis for Democratic maps, with the

difference in responsiveness to tides under Democratic and Republican waves for Democratic

gerrymanders significant at p<.01. Unfortunately, performing the same analysis for Republican

maps would involve drawing conclusions based on a very small number of elections11; the

difference in responsiveness by wave direction for Republican maps is not significant.

[Table 5 about here]

[Table 6 about here]

Although the sample size of elections, particularly Republican-wave elections, limits our

ability to demonstrate the different responses to waves under Democratic and Republican

regimes in a statistically robust way, we can at least observe these differences anecdotally. Table

6 depicts the percentage of close races in states with Democratic maps in the 1990’s and 2000’s,

and in states with Republican maps in the 1970’s and 2000’s.12 Elections with strong opposing

tides, where we would hypothesize a greater number of close races, are shown in italics.

17

With one exception, the results conform to our expectations. In both the 1990’s and the

2000’s, Democratic maps saw more close races in the two Republican wave elections (1994 and

2010), than other years during their respective decades. Republican maps also saw the greatest

number of close elections in post-Watergate election of 1974, and many more close election in

the Democratic waves of 2006 and 2008 than the previous two cycles. There were a high

number of wave elections under Republican maps during the 2010 Republican wave, likely due

to an number of races won by Democrats in 2008 turning flipping back to the GOP in those

states.13 Contrary to Yoshinaka and Murphy (2011), partisan gerrymanders do not increase

competition in years immediately following redistricting, but rather in years when tides turn

against the party in control.

Conclusion

The results in this paper provide evidence of both the limitations of partisan

gerrymanders and the effectiveness of nonpartisan reforms, results derived even in the absence of

information about what lines were actually drawn and how those lines specifically affected the

resulting campaigns. As hypothesized, seats gerrymandered by nonpartisan commissions appear

significantly more competitive than those drawn by bipartisan legislatures, whether

competiveness is measured by district partisan demographics or by vote margins in congressional

elections. Additionally, while partisan maps appear noncompetitive at the demographic level,

they generate greater competition in actual elections as national tides increase. Further, the

“pseudo-paradox” of greater national competition inducing less local competition, specifically

under partisan maps, suggests that partisan mapmakers are drawing lines to create safe seats

18

particularly in anticipation of close national conditions, somewhat oblivious to or discounting of

the possibility of uncertain future tides.

This work fits into a broader framework aimed at assessing the impact of gerrymandering

institutions, particularly moving toward bipartisan commissions, on voter welfare under different

representational interests. While the most recent election results may depict partisan

gerrymandering at its most powerful and insidious, a wider historical view presents a somewhat

different picture. Thus, these results suggest why Democrats may have reason to be hopeful

about their chances to retake control of the House at some point during the next decade, despite

the counter-majoritarian outcome in 2012 in which Republicans lost the national popular vote

but won the majority of seats. Because the national vote was extremely close, we might expect

very few close races in states with partisan control of redistricting (mostly Republican control in

the current decade). However, these same maps might see a great deal of competition and

turnover if Democrats can win a decent popular vote margin in the future, suggested by the fact

that President Obama won five Pennsylvania districts currently held by Republicans in 2012.

Gerrymandering has historically worked very for the controlling party when the national vote

was evenly split, but led to greater and often unexpected competitiveness as the national margin

increased. There is no reason to expect these same trends will not continue in the foreseeable

future.

19

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22

Figure 1. Partisan Balance of Districts in Four States, 2002 (Density Plot)

23

Figure 2. Close Races by Year

24

Figure 3. Close Races by Year and Gerrymandering Institution

25

Figure 4. Estimated Probability of Competitive Race by Redistricting Institution in Swing State in Tied Popular Vote Election

Notes: Entries represent the estimated probability of a race being won by less than 10% under various redistricting institutions, taken from model 2 in Table 3, if Statewide Competition and National Tides are set to 0. Error bars represent the 95% confidence interval of the probit coefficient.

26

Table 1. Effects of Gerrymandering Regime on District Level Competition

No South

District Level Presidential Competition (1) (2) (3)

Statewide Competition 0.31*** 0.32*** 0.32***

(0.028) (0.028) (0.036)

Democratic Gerrymander - 0.43 2.16**

(0.55) (0.90)

Republican Gerrymander - 1.78*** 2.11**

(0.66) (0.79)

Bipartisan Gerrymander - 1.15* 1.83**

(0.61) (0.75)

Court Gerrymander - 1.43*** 2.16***

(0.50) (0.73)

Nonpartisan Gerrymander -2.47** -2.01 -1.76

(1.26) (1.28) (1.38)

Constant 6.74 5.44 4.87

(0.30) (0.58) (0.78)

Observations 1,740 1,740 1,237 R-squared 0.069 0.076 0.065 Notes: DV is the absolute value of a district’s deviation from the national average in previous presidential elections, with lower values indicating swing districts. ** = p<.05, *** = p<.01

27

Table 2. Probability of Close Race Controlling for Statewide and National Competitiveness

No South No 1974

Pr(Close Race) (1) (2) (3) (4)

Statewide Competition -0.003 0.000 -0.001 -0.003

(0.003) (0.003) (0.003) (0.003)

National Tides 0.019*** 0.017*** 0.017*** 0.013**

(0.005) (0.006) (0.005) (0.006)

Year - - -0.002 -

(0.002)

Redistricting Year - - 0.004 -

(0.041)

Constant -1.18 -1.16 3.32 -1.15

(0.048) (0.055) (4.37) (0.050)

Observations 8,700 6,185 8,700 8,265 Notes: Entries are probit coefficients. Standard errors clustered by district interacted with decade. * = p< .10, ** = p<.05, *** = p<.01

28

Table 3. Probability of Close Race controlling for Redistricting Institution and State and

National Electoral Trend (Non-South Congressional Races 1972-2010)

No South W/Open

OLS Statewide

Means

OLS Statewide

Means Pr(Close Race) (1) (2) (3) (4) (5) (6)

Statewide Competition -0.0024 0.00030 -0.0025 -0.0021 -0.00022 -0.00012

(0.0031) (0.0036) (0.0032) (0.0031) (0.00083) (0.00084)

National Tides 0.021*** 0.019*** 0.020*** 0.035*** 0.0077*** 0.013***

(0.0045) (0.0054) (0.0046) (0.012) (0.0013) (0.0032)

Democratic Gerrymander -0.21*** -0.25** -0.21*** -0.13 -0.063*** -0.022

(0.063) (0.099) (0.065) (0.11) (0.017) (0.027)

Republican Gerrymander -0.15** -0.11 -0.12* -0.25** -0.046** -0.028

(0.071) (0.081) (0.073) (0.13) (0.018) (0.026)

Bipartisan Gerrymander -0.18** -0.21** -0.15** 0.014 -0.052*** 0.0025

(0.071) (0.081) (0.073) (0.13) (0.018) (0.029)

Court Gerrymander -0.024 -0.032 -0.018 0.058 -0.0071 0.00079

(0.060) (0.080) (0.062) (0.10) (0.016) (0.023)

Nonpartisan Gerrymander 0.36*** 0.34** 0.37*** 0.60*** 0.094** 0.16***

(0.13) (0.13) (0.13) (0.17) (0.043) (0.034)

Democratic Gerry*Tides - - - -0.014 - -0.0069**

(0.013)

(0.0035)

Republican Gerry*Tides - - - 0.012 - -0.0035

(0.014)

(0.0035)

Bipartisan Gerry*Tides - - - -0.031** - -0.0092**

(0.015)

(0.0036)

Court Gerry*Tides - - - -0.012 - -0.0011

(0.012)

(0.0029)

Nonpartisan Gerry*Tides - - - -0.046* - -0.013*

(0.027)

(0.0078)

Open - - 0.78*** - - -

(0.045)

Constant -1.07 -1.05 -1.20 -1.16 0.17 0.13

(0.075) (0.091) (0.078) (0.11) (0.021) (0.027)

Observations 8,700 6,185 8,700 8,700 1,000 1,000 R-squared - - - - 0.071 0.080 Notes: Entries in columns 1-4 are probit coefficients. Standard errors clustered by district interacted with decade. * = p< .10, ** = p<.05, *** = p<.01

29

Table 4. Coefficient for effect of National Tides on Close Races by redistricting institution (Congressional Races 1972-2010)

Institution Coeff. SE n Democratic .017** (.008) 2633 Republican .041*** (.010) 1552 All Partisan .027*** (.007) 4185 Bipartisan -.001 (.010) 2246 Nonpartisan -.010 (.027) 210 Small State .024 (.015) 598 Overall .019*** (.005) 8700 Notes: Entries are probit coefficients for the National Tides variable taken from Model 1 of Table 3, run under a subset of the data for each redistricting institution. * = p<.10, ** = p<.05, *** = p<.01

Table 5. Coefficient for effect of National Tides on Close Races under Democratic Gerrymanders (Congressional Races 1972-2010)

Institution Coeff. SE n Democrats win Popular vote .012 (.009) 2029 Republicans win popular vote .092*** (.023) 604 All elections .017** (.008) 2633 Notes: Entries are probit coefficients for the National Tides variable taken from Model 1 of Table 3, run under a subset of the data for each Democratic gerrymanders. * = p<.10, ** = p<.05, *** = p<.01

30

Table 6. Percent Close Races by Year and Gerrymandering Party

Close Races in Seats Drawn by Democrats

National GOP Year

Vote Margin

Seats % Close

1992

-5.3

119 16% 1994

6.9

119 20%

1996

-0.3

119 14% 1998

0.9

119 8%

2000

0.3

119 7%

2002

4.6

108 11% 2004

2.6

76 8%

2006

-7.9

63 5% 2008

-10.5

63 6%

2010

6.6

63 14%

Close Races in Seats Drawn by Republicans

Nat'l GOP Year

Vote Margin

Seats % Close

1972

-5.3

119 18% 1974

-16.6

119 28%

1976

-10.8

119 17% 1978

-8.7

119 17%

1980

-2.7

119 12%

2002

4.6

92 7% 2004

2.6

124 6%

2006

-7.9

137 12% 2008

-10.5

137 12%

2010

6.6

137 15%

31

Endnotes 1 Authors (2012) employs a simulation model to generate these hypotheses in a more rigorous

manner. Figures summarizing the results of these simulations are included in the Supplemental

Appendix. All of these predictions are consistent with existing literature on the effects of

bipartisan and nonpartisan institutions, and the implications of “dummymandered” partisan

maps. 2 It is possible that if many “naturally” competitive districts are drawn, these districts may

become non-competitive if tides favoring one party are strong enough. But the number of

nonpartisan commission states in our data set may be too small to draw strong conclusions on

this question. 3 Codings, listed in Supplemental Appendix A1, are mostly drawn from CQ’s Congressional

Districts in the 1970’s and subsequent volumes in this series. They were compared with the

codings from research such as Glazer (1987) and McDonald (2004) for robustness and

supplemented by other sources where the descriptions are ambiguous. 4 A handful of states are coded with more than one designation. This occurs most frequently

where a map is chosen by a court from among those proposed by the political parties. In such

cases, the congressional districts in this state are designated as being drawn both by a court and

by the party of the map chosen. 5 Because controls are statewide measures, the data set essentially describes the proportion of a

state elections that are close, weighted by the size of the delegation. An alternative specification

would be to make each of these proportions a data point, weight them by delegation size (so that

the impact of each individual election was still the same), and cluster by state interacted with

decade (yielding 800 data points and 160 clusters). As the DV would now be a proportion

(rather than a binary outcome), yet not properly described by a binomial distribution, it is more

difficult to determine an appropriate specification for the data formatted in this manner. I have

included such an analysis, where the proportion of close races is analyzed using OLS in Table 3,

alongside the probit models with individual districts as data points; the results are very similar

across models. 6 A binary variable for close races in assessing competition is used frequently in the literature

(e.g. Masket et al. 2012, Carson & Crespin 2004), and is chosen here because using continuous

vote margin leads results to be very sensitive to imputation decisions in unopposed races. I have

32

also tested an alternate definition of Close Race that additionally includes all instances of

turnover, with very similar results, shown in the supplemental appendix. About 18% of all

elections are Close Races under this alternate definition. 7 South is defined as the former Confederacy plus Oklahoma. All analyses in this article have

been checked excluding this region with substantively identical results; all results available from

author. 8 This lies in stark contrast with Table 1 showing that swing states tend to draw more

demographically competitive districts (as opposed to district that generate close election). 9 As an alternative to the Close Race dummy, this analysis can also be run with the overall vote

margin as the dependent variable. Using this DV, the effect of National Tides is negative and

significant at p<.05 when unopposed races are excluded, and significant at p<.10 when

unopposed races are included and counted as a 100% vote margin. Full results available from

author. 10 The interpretation is produced by adding the negative interacted coefficients for bipartisan and

nonpartisan maps to the positive uninteracted coefficient, producing a nonsignificant effect.

When the nonsignificant interacted coefficients for partisan maps are added to the significant

uninteracted coefficient, the sum remains significant and positive. 11 Due to the lack of Republican waves prior to 1994, and the lack of Republican gerrymanders

in the 1990’s, this essentially only analyzes the difference between the 2010 wave and the

smaller Republican victories in 2002 and 2004. Results in Supplemental Appendix. 12 Data for Democratic maps for the 1970’s and 1980’s are excluded because those decades had

no Republican wave elections at the congressional level. Data for Republican maps for the

1980’s and 1990’s are excluded because very few states had Republican-drawn districts during

that period (less than 40 total districts in any year). The number of seats changes during the

2000’s due to mid-decade redistricting in Texas and Georgia. 13 This outlier suggests that competitiveness may correlate not just from absolute tides, but tides

in one election relative to tides in the previous election. Result from regression models are

robust to inclusion of an auto-regressive term for national tides in the previous election cycle

(available from author on request); although this term does have an independent significant

effect of competition, it has no effect on the on the interactions of tides and districting regimes.