MidtermIRLS492
Safe Across the Border: The Continued Significance of the Democratic Peace When Controlling for Stable Borders*
Johann Park
Mississippi State University
and
Michael Colaresi
Michigan State University
We investigate the research findings reported in Gibler (2007) that suggest the democratic peace is in fact a spurious arti- fact of stable borders. If corroborated, this set of findings would mark an important reorientation for the field. However, we show that the research design used in Gibler (2007) suffers from several problems, including omitting the lower order terms of interaction variables and inappropriately assuming cross-dyad independence of artificially created dyadic democ- racy scores. Our replication and extension shows that even when controlling for stable border variables, democracy con- tinues to be a consistently useful predictor of international conflict. Further, the stable border variables themselves prove to be less consistent predictors of both peace and democracy as compared to previous research. These results suggest that both territorial issues and democracy can coexist as explanations for interstate bellicosity.
This research note explores one recent and important article that argues and reports evidence that territorial stability obviates the democratic peace for all pairs of states in the system. Douglas Gibler’s study (2007), “Bordering on Peace: Democracy, Territorial Issues, and Conflict,” finds that the democratic peace is epiphenome- nal to territorial issues. Specifically, Gibler argues (i) that stable borders increase the probability of a state being democratic; (ii) that stable borders decrease the probabil- ity of conflict using a sample of all pairs of states; and (iii) that democracy will be an insignificant predictor of peace between a pair of states when stable borders are included in the specification. For obvious reasons, the resounding evidence supporting these hypotheses in Gi- bler (2007) has received appropriate attention in the lit- erature. For example, in the sequel to one of the foundational books of conflict studies, The War Puzzle Revisited, Vasquez (2009: 370) regards Gibler’s study as “one of the few studies that successfully wipes out the sta- tistical significance between joint democracy and peace.”1
Gibler’s study stands in contrast to other research that has continued to find a robust relationship between democracy and conflict while controlling for territorial issues or contiguous relationships (Huth and Allee 2002; Colaresi, Rasler, and Thompson 2007; Reed and Chiba 2010). Engaging with this question is of cen- tral importance since, if Gibler’s analysis is sound, the near-law-like properties of the dyadic democratic peace will need to be amended and contextualized. As Gibler (2007: 529) argues, “my results suggest that what schol- ars know as the democratic peace is, in fact, a stable border peace.”
To probe whether this reorientation in theoretical out- look is empirically justified, we first attempted to locate the original data used in that article. Since the original data used in the published analyses predicting conflict and democracy has been lost,2 we next attempted to replicate Gibler’s research design using the coding rules outlined in the text.3 In our replication and extension, we are unable to find evidence that corroborates the finding in Gibler (2007) that controlling for stable borders ren- ders democracy an insignificant predictor of peace. Instead, we found clear evidence using Gibler (2007)’s own specification that higher levels of democracy con- tinue to decrease the probability of a militarized interstate dispute (MID).
Further, we uncover as part of our replication that the results presented in Gibler (2007) suffer from several research design shortcomings. The most important of these involve omitting the lower order terms when model- ing interaction effects (Braumoeller 2004; Brambor, Roberts Clark, and Golder 2006) and assuming in one set
Johann Park is an Assistant Professor at Mississippi State University. His research interests include international conflict, East Asian security, and quan- titative methods. Michael Colaresi is an Associate Professor at Michigan State University. His research interests involve the domestic politics of international conflict, the dynamics of conflict between rival states, and time series analysis. He has published two books.
* We would like to thank three anonymous reviewers and the editorial staff at ISQ. Additional thanks goes out to Paul Diehl and several members of the International Interactions team who took the lead on guiding the manu- script for the final round of reviews and revisions. Finally, Patrick James and Valentina Bali provided useful feedback throughout the process. The data from this project as well as an extensive online appendix are available at http://dvn.iq.harvard.edu/dvn/dv/Colaresi and at http://michaelcolaresi. org.
1 The findings in James, Park, and Choi (2006) lend some credence to this inference since they find an inconsistent effect for democracy on pacify- ing territorial disputes in the Western Hemisphere, although more recent work in Park and James (2014) shows a more consistent pacifying effect for democracies within territorial disputes.
2 Private correspondence with Douglas Gibler. 3 We describe our coding steps in the Web appendix and the replication
files are available online.
Park, Johann, and , Michael Colaresi. (2014) Safe Across the Border: The Continued Significance of the Democratic Peace When Controlling for Stable Borders. International Studies Quarterly, doi: 10.1111/isqu.12114 © 2014 International Studies Association
International Studies Quarterly (2014) 58, 118–125
of specifications that democracy scores are independent across dyads in a given year even with a common mem- ber,4 among other limitations. We present models that first attempt to replicate Gibler (2007)’s specification, continuing to omit the problems summarized above. We then extend the conflict model, in turn, to include the lower order terms and additional control variables. Simi- larly, we offer a model of democracy that does not suffer the same cross-sectional dependence problem as found in Gibler (2007).
Unlike the analyses presented in Gibler (2007), the findings herein reveal that the various measures for bor- der stability perform inconsistently in predicting either armed conflict or democracy, while in every specification predicting the probability of conflict, democracy contin- ues to be a substantively and statistically significant pre- dictor of peace. Additionally, we show that the analysis of joint dyadic democracy as a dependent variable suffers from extreme residual correlation. When our more appropriate monadic model of democracy is estimated, again adding the lower order terms, stable borders prove to be as inconsistent predictors of democracy as they were with conflict.5
Border Problems
Here, we highlight two important problems with the research design presented in Gibler (2007). First, Gibler (2007) neglects to include the lower order terms of the interaction variables in both the analyses of dyadic democracy and militarized disputes. While using a sample of all dyads, Gibler (2007) coded his seven border stabil- ity variables as products of land contiguity (a dichoto- mous variable) times the relevant other measures (parity, number of unbroken years of peace, civil war status, dyad
age, relative colonial history, a state’s relative ethnic lin- eages, and territorial similarity).6 However, the seven vari- ables themselves, un-interacted with land contiguity, are absent from all specifications.
Omitting these terms atheoretically assumes in the conflict equations in Table 3 of Gibler (2007) that capa- bility ratios, years since the last MID, civil war onset, duration of the dyad, relative colonial history, and the relative identity of the populations all jointly have no effect on conflict propensities for non-contiguous dyads. Brambor et al. (2006) and Braumoeller (2004) cogently argue that omitting lower order terms7 can bias the inferences one makes on the multiplicative interactions. In this case, numerous studies suggest that capability ratios (Reed and Chiba 2010), colonial history (Conge 1996; Bernhard, Reenock, and Nordstrom 2004), peace years (Beck, Katz, and Tucker 1998; Dafoe 2011), civil wars (Gleditsch, Salehyan, and Schultz 2008), topogra- phy and terrain (Underwood and Guth 1998; Reiter and Stam 2002), and the age of states (Maoz 1996) are likely to matter for non-contiguous states. Omitting these terms can bias inferences, sometimes severely. In fact, Brambor et al. (2006: 66) write, “Analysts should include all constitutive terms when specifying multiplicative interaction models except in very rare circumstances.”8
Second, the analysis of joint dyadic democracy in Gibler (2007; Table 2) suffers from extreme residual cross-sectional dependence. This is due to the research design strategy employed, where it is assumed that any unmodeled change in the democracy score within a dyad has no effect outside of that specific dyad, even in dyads that involve that same state. In effect, Gibler (2007) assumes that France has a different democracy score when interacting with Germany as compared to Spain in any given year. This cannot be true given the measure- ment of democracy at the monadic level. This biases the standard errors downward and invalidates inference (Hsiao, Pesaran, and Pick 2012).9
Replicating and Extending “Bordering on Peace”
To analyze whether we could first replicate10 the insights of Gibler (2007) and if so, whether the inferences were robust to corrections for the problems noted above as well as alternative specifications, we constructed a new data set according to the rules specified in that paper.11
4 This assumption implies that Egypt becoming democratic will only affect the Egypt–Israel dyad but not any other dyadic paring involving Egypt (for example, Egypt–United States, Egypt–UK, etc.). However, as we show, given the coding of the joint democracy dependent variable, this cannot be true by definition.
5 Recent work by Gibler and Tir (2010) builds upon the research in Gibler (2007) but does not provide any additional findings of the insignifi- cance of the democratic peace. This later article reports evidence that a peaceful cessation of territorial disputes is correlated with more democracy. There is no analysis of conflict onset in this later article. Owsiak (2012) also attempts to build upon Gibler (2007), but does so only using a sample of con- tiguous states. In private correspondence, Professor Gibler has suggested that he now believes that only a subset of contiguous-by-land pairs of states should be used to analyze whether the democratic peace holds when controlling for his variables of interest. As we argue below, this post hoc change in research design is not useful because the findings and specifically the published con- clusions in Gibler (2007) are not conditional on contiguity—all dyads are uti- lized for the analysis and the conclusion that the Gibler (2007:529) article explicitly draws is “that what scholars know as the democratic peace is, in fact, a stable border peace.” One cannot make this unconditional statement about the democratic peace without including both contiguous and non-contiguous dyads in the study. Additionally, analyses lacking non-contiguous dyads ignore one of the major problems inherent in the interpretation of the findings in Gibler (2007) that we identify here. Many of the proxy measures for stable borders, such as ethnic groups living in both members of a dyad, the presence of a civil war, and colonial history, operate similarly in both contiguous and non-contiguous relationships. Therefore, borders cannot explain their effect on peace, since even states that do not share borders evince the same patterns of war and peace, conditional on the covariate of interest (for example, see Figure 2). Omitting all non-contiguous states makes the identification of this problem with proxy variables impossible without adding back the non-contigu- ous observations. These limitations are in addition to legitimate concerns about the reduced power in a conditional analysis using only contiguous dyads as well as mistaking a failure to reject the null for the acceptance of the null hypothesis.
6 The specific operationalizations of these concepts are discussed in the online appendix.
7 These are sometimes referred to as main effects or constituent terms. 8 Brambor et al. (2006: 69) suggest that the only case for omitting lower
order terms is when two conditions are simultaneously met: (i) there must be a strong theoretical reason for omitting the lower order term of an interac- tion, a condition that is obviously not met here, and (ii) that the full model is estimated with the lower order terms and these lower order terms are all esti- mated to have narrow confidence intervals that include zero. We show below that this last condition is also not satisfied in the present case.
9 Due to space constraints, we present evidence of this problem, as well as a correction for it, in the Web appendix.
10 Here, we define replication along the lines of King (1995: 451). This is in contrast to “duplication,” which is here impossible due to the lost data.
11 We would have strongly preferred to use the original data source, but since this data are now lost, we collected our own based on what was written in Gibler (2007).
Johann Park and Michael Colaresi 119
The details of our replication are included in the Web appendix and are available online.12
The Effect of Democracy on Peace
The first replication model13 is presented in the first col- umn (Model 1) in Table 1. Unlike in Model 4, Table 3 in Gibler (2007), the coefficient for democracy is negative and statistically significant here. As noted previously, this model neglects to include the lower order terms for the seven stable border variables: territorial similarity, ethnic group linkages, civil war, colonial history, power parity, time since last MID, and the age of the dyad. Addition- ally, there is some uncertainty as to whether the model in Gibler (2007) included peace-year splines.14 Thus, we have also estimated the specification in Model 1 adding peace-year splines, but not lower order terms. Since these results are so similar to those reported in Model 1, we do not present the full set of parameters here.15 In this case, the coefficient for the weak link democracy score is �0.040, with a 95% confidence interval of (�0.028, �0.052), and a p-value much lower than .001.
Models 2, 3, and 4 add the lower order terms for the previously interacted border stability variables. These specifications differ only in the way the peace-year splines are included in the specification and the number of addi- tional control variables used. Specifically, Model 2 adds the lower orders and estimates coefficients for the nonlin- ear peace-year splines that are not interacted with land contiguity. Model 3 adds the full interaction between the peace-year splines and land contiguity.16 Model 4 includes variables measuring the number of previous MIDs, whether at least one member of the dyad is a major power, and a dummy variable for the post-Cold War world.17
In every specification, democracy remains a significant predictor of peace, in contrast to the findings
in Gibler (2007).18 Because of substantial ambiguity in the coding rules that were used in Gibler (2007), we also ran seven other specifications that are detailed in the Web appendix. In all of these, democracy remains a sig- nificant predictor of peace. Further, the difference in the Akaike (AIC) and Bayesian (BIC) information criteria among the models in our Table 1 strongly support Model 4, which includes the lower order terms, nonlinear deter- ministic trends, and additional covariates, as the best fit- ting model. This suggests that several sets of important factors were omitted from the Gibler (2007) specifica- tion.19 These findings remain robust when we change from a weak link measure of democracy to a dichotomous measure. Due to space constraints, we summarize these findings across another 11 specifications in the online appendix.20
Additionally, the effect on democracy is of substantive interest across the specifications. The first plot in Figure 1 plots the predicted probability of conflict as democracy increases for noncontiguous states across each model. Model 1 shows only a modest slope, due to the zero restrictions within the original Gibler (2007) specifi- cation that this model replicates. Specifically, variables such as parity, peace years, dyad years, and others are assumed to only have a nonzero effect within contiguous dyads and have an exactly zero effect in non-contiguous dyads. The first plot in Figure 1 makes clear that these restrictions not only decrease the fit of the model, but also significantly depress the underlying expected proba- bility of conflict for non-contiguous dyads, in general. Once we relax these atheoretical restrictions, the baseline probabilities rise as in Models 2, 3, and 4. Further, the second plot in Figure 1 illustrates that the relative risks across the models are consistent. In each case, moving democracy from one standard deviation above the mean to one standard deviation below the mean, a decrease of approximately 11 points on the 21 point scale, is expected to increase the probability of conflict by a factor of approximately 1.5 or 50%, regardless of specification.21
In summary, across 23 specifications reported here and in the online appendix, democracy continues to predict dyadic peace at a reasonable level of statistical signifi- cance, contra the findings in Gibler (2007), Table 3. We find no evidence that stable borders render the demo- cratic peace spurious.
12 Gibler (2007) includes a few models that subset the analysis by Cold War/post-Cold War period. We did this also. These models supplied no addi- tional support for the inferences in Gibler (2007). However, some of inconsis- tent findings, such as territorial similarity leading to less conflict, rather than more, were stronger in the post-Cold War period. These models also imply three-way interactions that needlessly complicate the inferences. Further AIC and BIC values were lower, indicating an improved fit relative to the number of parameters, for the non-stratified models.
13 Throughout, we do not report robust standard errors that are clustered by dyad since it does not appear that Gibler (2007) used them. We have run every model with robust standard errors clustered by dyad. These do not change our inferences for democracy, but they do weaken the stable border hypotheses further.
14 In private correspondence, the previous author has noted that he did use the nonlinear spline coefficients, but neglected to mention them in the article or report them in the tables.
15 They are included in the online appendix. 16 This is done because Brambor et al. (2006) and others suggest that if
two concepts are thought to interact, in this case peace years and contiguity, then each variable measuring those concepts should also be interacted.
17 The spline coefficients and standard errors in Models 2, 3, and 4 are multiplied by 100 so the significant digits can be discerned. The definition of a major power comes from Correlates of War Project (2008), which follows the definitions in Singer and Small (1972). More details are provided in the Web appendix.
18 The difference in the finding could come about from coding differ- ences. We are making our data publicly available so that any mistakes we might have made can be corrected for the empirical record. One contradic- tion between our replication and Gibler (2007)’s reported results in Table 3 is the difference in the number of observations. Gibler provides the “number of contiguous dyads” for the 1946–1999 period as 504,376 (for Model 1 in his Table 3) which cannot be accurate since the number of (land) contiguous dyad years in the system would be equal to 11,394 excluding joiner dispute dyads and ongoing dispute years based on EUGene version 3.2 calculations (Bennett and Stam 2000). Even if this is meant as the total number of dyads, it is too high given the missing observations of GDP and the polity scores. Fur- ther, when the stable border variables are coded, the number is reported to be 364,779, whereas we have 379,821 non-missing observations as in all of our models, Table 1 above.
19 The differences in BIC values of well over 100 are extremely strong evi- dence in favor of each model over Model 1. Further, the BIC penalizes the additional parameters in each successive specification more than the AIC, but still prefers the more complex models in this case.
20 This dichotomous measure was used in Gibler (2007) for the model predicting democracy, but not in the model using democracy to predict peace.
21 The findings for the dichotomous measure of democracy tell a similar story and are available from the authors.
120 Safe Across the Border
TABLE 1. Logistic Regression Results Predicting Militarized Interstate Dispute onset, 1946–1999
Model 1 Model 2 Model 3 Model 4
Intercept �6.811 (0.057)* �4.819 (0.114)* �4.736 (0.122)* �5.017 (0.130)* Lowest Dem �0.032 (0.006)* �0.043 (0.006)* �0.042 (0.006)* �0.030 (0.007)* Lowest GDP 0.326 (0.038)* 0.236 (0.041)* 0.236 (0.041)* 0.158 (0.041)* Contiguous 4.512 (0.117)* 3.088 (0.147)* 2.954 (0.166)* 2.654 (0.172)* Parity �0.526 (0.178)* �0.529 (0.178)* �0.133 (0.182) Peace Yr. (Linear) �0.347 (0.019)* �0.375 (0.028)* �0.350 (0.028)* Peace Yr. (Spline 1) �0.016 (0.002)* �0.018 (0.003)* �0.017 (0.003)* Peace Yr. (Spline 2) 0.007 (0.001)* 0.008 (0.002)* 0.008* (0.002) Peace Yr. (Spline 3) �0.001 (0.001) �0.001 (0.001) �0.001 (0.002) Civil War 0.449 (0.194)* 0.429 (0.194)* 0.460 (0.197)* Dyad Age 0.027 (0.001)* 0.027 (0.001)* 0.018 (0.001)* Colonial History �0.131 (0.163) �0.120 (0.163) �0.042 (0.164) Ethnic Border �0.427 (0.586) �0.454 (0.586) �0.129 (0.587) Terr. Similarity 0.208 (0.043)* 0.206 (0.043)* 0.159 (0.043)* Previous Disputes 0.153 (0.009)* Post-Cold War �0.593 (0.094)* Major Powers 1.079* (0.088) Parity 9 Contig 0.243 (0.154) 0.691 (0.238)* 0.698 (0.238)* 0.475 (0.239)* Peace Yr.(L)9 Contig �0.086 (0.005)* 0.016 (0.005)* 0.065 (0.038) 0.084 (0.039)* Spline 1 9 Contig 0.003 (0.004) 0.003 (0.004) Spline 2 9 Contig �0.001 (0.003) �0.001 (0.003) Spline 3 9 Contig �0.001 (0.001) �0.001 (0.001) Civil War 9 Contig. 0.881 (0.162)* 0.333 (0.255) 0.358 (0.255) 0.285 (0.264) Dyad Age 9 Contig. 0.004 (0.001)* �0.024 (0.002)* �0.023 (0.002)* �0.027 (0.002)* Col. Hist. 9 Contig. 0.043 (0.104) 0.211 (0.195) 0.192 (0.195) 0.235 (0.198) Eth. Border 9 Contig. 0.222 (0.126) 0.659 (0.600) 0.683 (0.600) 0.740 (0.601) Terr. Sim. 9 Contig. �0.020 (0.048) �0.250 (0.066)* �0.247 (0.066)* �0.260 (0.068)* N 379,821 379,821 379,821 379,821 AIC 11,900.373 10,631.691 10,633.670 10,136.269 BIC 12,377.661 11,542.877 11,675.026 11,307.794 log L �5,906.187 �5,231.845 �5,220.835 �4,960.134 Standard errors in parentheses. Bolded rows represent concepts where the authors could corroborate the inferences from the original article. *Indicates significance at p < .05. Model 1 replicates the specification described in Gibler (2007). Model 2 adds the omitted main effects as well as nonlinear spline terms for peace years. Model 3 adds the full interactions between contiguity and both the linear and nonlinear terms for peace years, while Model 4 includes additional control variables.
10 5 0 5 10
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Model 1 Replication
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PY Splines Model 4
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FIG 1. The predicted probabilities and relative risks for the lowest democracy variable across the four models. The first plot traces the probabil- ity of conflict across the values of the lowest democracy score. All continuous variables are held at their mean, dichotomous variables at their mode, the comparisons are for non-contiguous states. The second plot presents the relative risk of conflict for a dyad with a lower democracy score one standard deviation below the mean to that with a lower democracy score one standard deviation above the mean. A relative risk
more (less) than one means a higher (lower) risk of conflict
Johann Park and Michael Colaresi 121
The Effects of Stable Borders on Peace
Having established the robust substantive and statistical significance of the democratic peace across several specifi- cations, including a direct replication of the results reported in Gibler (2007), Table 3, Model 4, we now turn to an analysis of the stable border variables.22 It could still be the case that while democracy remains a consis- tent predictor of peace, the stable border hypotheses relating border strength and salience are independently supported in the data. We also investigate whether possi- ble multicollinearity between the stable border variables in Gibler’s specification and democracy is masking the effect of the stable border concepts.
Again, we look at the stable border variables across the four specifications presented above, as well as a fifth that excludes democracy from the specification. The coeffi- cients, standard errors, and fit statistics for this last specifi- cation, omitting democracy, are included in the online appendix. Across the models in Table 1, when controlling for democracy, the stable border variables perform incon- sistently. We find in our replication that when the lower order terms are omitted from the model as in Gibler (2007), and thus assumed to be zero, it appears that three out of the seven stable border variables—linear peace years, civil war onset, and dyad duration—significantly pre- dict the likelihood of conflict. Gibler (2007) reports four significant variables, and his set differs slightly from ours. He reports that parity, linear peace years, civil wars, and ethnic borders are significant.23 Regardless of these differ- ences, the specification forces us to assume that concepts such as power parity, civil wars, peace years, state age, ter- rain similarity, and ethnic linkages have no effect on non- contiguous dyads, with certainty (Brambor et al. 2006: 26).24 This assumption is of course testable. As noted, Mod- els 2–4 in Table 1 relax and test this assumption by allow- ing these variables to affect non-contiguous dyads.
Indeed, as can be seen across the specifications in the above tables, parity, linear peace years, civil war, and dyad duration, each is estimated to significantly predict con- flict and peace in dyads that are non-contiguous.25 Wald tests of the assumption that all of these lower order terms are simultaneously equal to zero in Models 1, 2, and 3 of Table 1 have test statistics of 1192.2, 1533.8, and 797.6, all with p-values far below .001. This is very strong evi- dence against the zero restrictions on the effect of the lower order terms in Gibler (2007).
More substantively, we now have evidence of the prob- lems with omitting lower order terms—if the strict zero restrictions are not met, inferences can be extremely mis- leading. The significance of the product of civil war and contiguity in Table 3 of Gibler (2007), without the lower order term, is interpreted by the original author as evi- dence that civil wars in contiguous states destabilize bor- ders and increase the probability of conflict. However,
when the lower order term is included, there is no evi- dence that civil wars increase the propensity for MID onset any more in contiguous states than non-contiguous states. Therefore, there is no evidence to support the hypothesis that borders play a role in the interpretation of the effect, since the effect is constant regardless of whether the dyad shares a land border or not.26 Across Models 2 through 4, territorial similarity, measured by Gibler as states in a dyad that have similar percentages of mountainous terrain, does appear to interact with conti- guity, since the interaction coefficient is significant, but that effect is in the opposite direction as hypothesized in Gibler (2007). The estimated effect in Model 4 suggests that territorial similarity decreases the log-odds of conflict for contiguous states,27 as opposed to increasing the pro- pensity for conflict for neighboring states as hypothe- sized. In contrast, territorial similarity is estimated to increase bellicosity for non-contiguous dyads.28
It is easiest to see these relationships when using the pre- dicted probabilities to plot the relative risk across contigu- ous and non-contiguous dyads for the stable border variables as in Figure 2. This figure uses the coefficients from the best fitting model (Model 4) and presents the rel- ative risk of a conflict in a contiguous dyad versus a non- contiguous data, for a given change in the variable of inter- est.29 A relative risk of one tells us the probabilities are equal, as denoted by the black horizontal line on the plots. The final (third from the left) bar plots the ratio of esti- mated relative risks, specifically the relative risk for a con- tiguous dyad divided by the relative risk for a non- contiguous dyad.30 Again, a ratio of one implies the same effect in contiguous and non-contiguous settings.31 This figure projects the finding from Table 1 on to the relative risk quantity of interest. Here, we see that while civil wars and ethnically divided groups32 within a dyad increase the risk of conflict in contiguous states, we fail to reject the null hypothesis, at the 0.05 level, that these variables have the
22 Note that we are interested in whether the discrete first differences across contiguous contexts (contiguous dyad or not) are distinct. This is akin to estimating the difference in the treatment effects across contexts; see Puh- ani (2008).
23 Gibler (2007: 527) writes that while dyad duration and colonial history are not significant in the table reported on page 528, in separate analyses that omit the democracy measure these variables regain significance. We return to this point below when we present a model that omits democracy as a covari- ate.
24 We discuss the inferential consequences of omitting relevant lower order terms in the online appendix.
25 Here, we are on the log-odds scale.
26 Note that we are discussing effects on the log-odds scale since the model in Gibler (2007) and many other conflict studies explicitly assume the effects of variables have linear effects on the log-odds of disputes. Below we discuss the substantive impact of these variables on the relative risk of conflict which is a more intuitive quantity of interest.
27 The lower order parameter for terrain similarity is estimated as 0.16 and the interaction term is �0.26. The sum of these effects �0.1 has an asso- ciated p-value of .055 and is evidence that as terrain similarity for contiguous states increases, the probability of conflict decreases.
28 This could be measuring a regional or proximity effect or might be an artifact of other omitted factors.
29 The simulated changes are 0–1 for dummy variables and from one stan- dard deviation below the mean to one standard deviation above the mean for continuous covariates.
30 For example, for civil war, a relative risk of 2 in contiguous dyads means that the estimated probability of conflict is twice as high for a contigu- ous dyad involved in a civil as compared to a contiguous dyad not involved in a civil war. A ratio <1 means that the probability decreases by that factor.
31 The ratios are important here because the logit model used in Gibler (2007) is linear on the log-odds scale and thus, when the coefficients are ex- ponentiated, they provide odds ratios. The odds ratios are useful approxima- tions to the relative risks, but since we can directly simulate the relative risks as the quantity of interest, we present those here. The ratio of the relative risks tells us specifically whether the change in the propensity for conflict across two settings of a variable, all else set equal, is different in contiguous versus non-contiguous dyads. Bennett and Stam (2004: 67–69) make the case, specifically for conflict research, that relative risks are useful quantities of interest.
32 We also tried the alternative coding of divided ethnic groups as dis- cussed in the appendix. In no case did this lead to additional support for the stable border hypotheses. Similarly, un-logged values of parity and terrain sim- ilarity did not produce additional evidence for the theory.
122 Safe Across the Border
same effect on contiguous and non-contiguous dyads. The previous omission of the main effects misattributed these relationships purely to contiguous dyads, by assumption.33
Suggesting democracy as an instrument for the effects of stable borders, Gibler (2007: 527) reports in the text that all seven of his border stability variables are statisti- cally significant and in the predicted direction when democracy is excluded from the specification. To investi- gate whether democracy was masking the effect of the sta- ble border variables in the above analysis, we again ran the best fitting model (Model 4) without democracy.34
These results, reported in the online appendix, are simi- lar to our previous model and slightly weaker for the sta- ble border variables, as now the product of parity and contiguity fails to be statistically significant at the 0.05 level. Therefore, even when democracy is excluded from the model and the relevant covariance between democ-
Contig. Non−contig. Ratio
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0 1
2 3
4 5
6 7
R R C on tig
R R N o n
Contig. Non−contig. Ratio
Parity (mean−sd to mean+sd)
R R
= p( y
= 1| x 1 )
p( y
= 1| x 0 )
0 1
2 3
4 5
0 1
2 3
4 5
R R C o n tig
R R N on
Contig. Non−contig. Ratio
Terr. Similarity (mean−sd to mean+sd)
R R
= p ( y
= 1| x 1 )
p( y
= 1| x 0 )
0 1
2 3
4 5
0 1
2 3
4 5
R R C on tig
R R N on
Contig. Non−contig. Ratio
Dyad Duration (mean−sd to mean+sd)
R R
= p( y
= 1| x 1 )
p( y
= 1 | x 0 )
0 1
2 3
4 5
0 1
2 3
4 5
R R C on tig
R R N on
FIG 2. The relative risk of conflict in contiguous and non-contiguous dyads across changes in the stable border variables. The substantive changes in each variable are listed in parentheses. The dark solid, light solid, and dashed bars represent the 95% confidence intervals for the effect of the relevant variable in contiguous dyads, non-contiguous dyads, and the ratio of the two, respectively. No substantive change would
be reflected in a relative risk of one; relative risks lower than one reflect decreases in the risk of conflict
TABLE 2. Comparing The Hypotheses and Finding on Conflict Behavior in Gibler (2007) With the Finding of The Best Fitting
Analysis Here
Variable
Gibler (2007)
Expected Reported Our Findings
Territorial Similarity
Positive Positive* Negative
Ethnic Border Positive Positive Not Significant Civil War Positive Positive Not Significant Colonial History Positive Positive* Not Significant Power Parity Positive Positive Positive Peace Time Negative Negative Nonlinear Dyad Duration Negative Negative Negative
The last column represents the direction and significance (at the 0.05 level) of the interaction coefficients in Model 4 of Table 1 above, which are also reflected in Figure 2 and the nonlinear effect of the peace-year splines (shown in the online appendix) above *Represents a result reported in the text (527) but not reported in Table 3 (528) in Gibler (2007).
33 The conditional nonlinear relationship between peace years and con- flict is illustrated in the online appendix, due to space constraints.
34 It should be said that we found no evidence of multicollinearity between democracy and any of the stable border variables in the replication analysis.
Johann Park and Michael Colaresi 123
racy and each stable border variable is apportioned in full to the stable border concept, we continue to find only ambiguous support for the stable border hypotheses.
Table 2 summarizes our findings on the stable border indicator variables and contrasts our findings in Model 4 of Table 1 with those reported in Gibler (2007:527). While Gibler (2007) concludes that all seven of his bor- der stability concepts contribute to a statistically signifi- cant and coherent understanding of conflict, we find that the results are much less consistent.35 Only dyad duration and power parity supply evidence that is consistent with the stable border hypotheses. The other five indicators are in the wrong direction or show no evidence of affect- ing the propensity toward conflict differently in contigu- ous dyads as compared to non-contiguous dyads when appropriate controls and lower order terms are included in the model. Similarly, years of peace, when appropri- ately measured with splines and interacted with land con- tiguity, showed inconsistent differences over time.36
This does not suggest that stable borders do not matter for conflict. On the contrary, we find evidence that parity between neighbors and the presence of new neighbors increases the probability of conflict over and above what one would expect if those two states were not neighbors. However, each of the other stable border concepts appears to be measuring non-border effects since it is contradictory to infer border stability evidence from coef- ficients where we cannot reject the null hypothesis that they operate equally regardless of whether states share a border or not.
The Effects of Stable Borders on Democracy
Due to space constraints, we summarize our findings on the effects of the stable border variables on democracy in this section. More information and details are provided in the online appendix. Using our data, we replicated the specification in Gibler (2007), Table 2, Model 4, which estimated the effect of stable borders on democracy using dyad-year data. We added main effects to this specifica- tion. In this case, only two out of the seven border stabil- ity (dyad duration and colonial history) variables lead to statistically discernible changes in democracy levels for contiguous states. As noted, this model suffers, however, from severe cross-sectional dependence, with extreme error correlations across dyads within a given year approaching 1. These error correlations are assumed to be 0 in Gibler (2007) (see the Web appendix).
To correct for these problems, we ran a monadic analy- sis of the democracy equation with a monadic measure of each stable border variable included.37 Our unit of analy-
sis is the state-year, and the time domain was again 1946– 1999. The details of our model, as well as the table of result, are included in the online appendix.
The findings reveal that across different specifications, only a small subset of the parameters associated with the border stability variables implied support for the evidence in Gibler (2007).38 One border stability variable that does remain significant in our analysis is peace years. Thus, we have come full circle. The covariance between democracy and peace is evident in this data. This suggests to us that further research on the two-way reciprocal relationships between democracy and peace may be empirically fruit- ful.39
Table 3 summarizes our findings40 predicting democ- racy as compared to those reported in Gibler (2007). As in the conflict analysis, we were unable to reproduce the strong support Gibler (2007) found for the stable border hypotheses. In fact, we present evidence not only that democracy continues as a useful inhibitor of conflict when stable border variables are specified, but that stable border variables are themselves inconsistent predictors of democracy and conflict.
Conclusion: Territory and Democracy, Together Again
Our results do not support the claim that the democratic peace is in reality a stable border peace. In fact, the sta- ble border variables presented in Gibler (2007) are inter- esting but inconsistent predictors of both peace and democracy. In contrast, the democratic peace remains robust when controlling for stable borders. In other work, we do find that territorial disputes themselves, as coded by Huth and Allee (2002) are a significant predictor of armed conflict, although these spatial claims also do not obviate the effect of democracy on peace (Park and James 2014). Therefore, we suggest that future research
TABLE 3. Comparing the Hypotheses and Finding on Democratiza- tion in Gibler (2007, Model 4, Table 2) With The Finding of Our
Logit Model
Variable
Gibler (2007)
Expected Reported Our Findings
Territorial Similarity Negative Negative Not Significant Ethnic Border Negative Negative Not Significant Civil War Negative Negative Not Significant Colonial History Negative Negative Not Significant Power Parity Negative Positive* Not Significant Peace Time Positive Positive Positive Border Age Positive Positive Not Significant
The last column presents the direction and significance (at the 0.05 level) of the coefficients in the logit model (our model 2) *Represents a result reported in Table 2 in Gibler (2007:525) that seems to have been misinterpreted in the text (see page 524).
35 We also ran the specifications in Models 1, 2, and 3 without the democ- racy variable. In each of these cases, no more than three stable border vari- ables were ever significant at the 0.05 level and in the predicted direction, and again each fit was substantially inferior to Model 4.
36 Specifically, the model fit improved with the inclusion of the interac- tion between contiguity and the peace-year spline variables, but the effect of these variables was not monotonic nor was it substantively distinct from the effect of peace years for non-contiguous dyads when analyzing the relative risk of conflict over the range of peace years in the sample.
37 The details are included in the Web appendix. We also estimated mod- els using the continuous measure of democracy. The results were even less supportive of the stable border hypotheses concerning democracy. None of the stable border variables were individually significant at the 0.05 level, and the seven variables together generated a F statistic of F(7, 5,009) = 0.75 with an associated p-value of .629. Therefore, we fail to reject the null using the continuous measure of the democracy in an OLS model that all of the stable border variables are simultaneously equal to zero.
38 When we estimated transitions to democracy, rather than the presence of democracy, none of the border stability parameters were significant at the 0.05 level. Since democracy is a measurement that varies across states in a given year, it is not possible for dyadic democracy (two countries being demo- cratic or not) to change without a monadic change (at least one of the states changing regimes) across all its dyadic partners in the data.
39 Of course, identifying the parameters of each structural equation is a challenge as is cross-level inference. As we note in the appendix, our monadic model can be used in an equation-by-equation estimation strategy since an instrument for dyadic democracy can be created from the monadic model.
40 These findings are reported in the online appendix.
124 Safe Across the Border
should focus on deepening our understanding both of the territorial causes of war as well as the domestic politi- cal determinants of bellicosity.
Our research will not be the last word on the trilateral interaction between territorial issues, democracy, and con- flict, nor should it be. There are several limitations to the present study. The most important is that the original data from Gibler (2007) were lost and therefore could not be used. However, our replication data are available and will allow the debate to continue on in future studies.
Continued research into the interstices of territorial claims and regime type is likely to lead to important breakthroughs in conflict research. Territorial explana- tions do not have to render the democratic peace insig- nificant in order to themselves be significant (Reed and Chiba 2010). Further, democratic peace theories do not have to render territorial explanations moot. In fact, Colaresi et al. (2007), Senese and Vasquez (2008), and Dreyer (2010), each using different research designs, find substantively meaningful effects for territorial issues. Recent work by Owsiak (2012), using a sample of contiguous states, finds parallel support both for the pacifying effect of democracy and bellicosity of territorial disputes.
Finally, we believe this exploration of previous research underscores the importance of replication and extensions generally. As estimation procedures, data coding and management, and statistical interpretation grow more complex, the chances for mistakes increase. Replication allows us as a discipline to probe the usefulness and robustness of previously published findings that may be sensitive to reasonable changes in research design strat- egy (Dafoe 2011:259; Park 2013).
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Supporting Information
Additional Supporting Information may be found in the online version of this article:
Appendix. Safe Across the Border: Web Appendix.
Johann Park and Michael Colaresi 125
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