1. Coup-proofing: conceptualization and relevant indicators

A coup d’état is a sudden and violent takeover of a government by the military, typically with the aim of ousting the current political leadership. Military coups often involve the use of force, and the military leaders who execute the coup frequently assume control of the government (Luttwak, Reference Luttwak1979; Quinlivan, Reference Quinlivan1999; Singh, Reference Singh2014). Huntington (Reference Huntington1957)'s seminal work on civil–military relations argues that professionalizing the military can make it subservient to civilian authority. Nonetheless, a group of scholars indicates that military professionalism does not always imply military submission to civilian leadership, and that in the absence of an effective constraint mechanism, a professionalized military can overthrow civilian leadership (Finer, Reference Finer1974; Feaver, Reference Feaver1996; Janowitz, Reference Janowitz1961).

Political leaders implement coup-proofing strategies to prevent the military from intervening in politics using force. However, the definition of coup-proofing varies among scholars (Reiter, Reference Reiter2020). Some studies define it as measures to reduce the military's coup-making capabilities by counterbalancing and purging military officers (Sudduth, Reference Sudduth2016, Reference Sudduth2017b; De Bruin, Reference De Bruin2020a). Other scholars suggest that coup-proofing also includes co-optive strategies to lower the military's motivation to stage a coup by providing material and political benefits (Powell, Reference Powell2014; Powell et al., Reference Powell, Faulkner, Dean and Romano2018; Brooks, Reference Brooks2019; Reiter, Reference Reiter2020).

Our research primarily focuses on the aspects of coup-proofing that limit the military's ability to stage a coup and increase the cost of doing so. As Sudduth (Reference Sudduth2016: 4) intuitively notes, co-optive or spoiling aspects of coup-proofing, such as providing funding and granting access to the military's national policy decision-making, increase the military's coup-making power, thereby increasing the likelihood of a successful coup (Svolik, Reference Svolik2013; Acemoglu et al., Reference Acemoglu, Ticchi and Vindigni2010). A key objective of coup-proofing is not only to prevent a coup from being attempted but also to thwart its “success” if it is carried out. Therefore, coup-proofing should be conceptualized as the degree to which the military's ability to execute coups is diminished while the associated costs of coup attempts are increased. This conceptualization aligns with the overarching objective of coup-proofing, which seeks to prevent both the attempt and the successful execution of a coup.

It is noteworthy to clarify why we think the “extent of coup-proofing” is the appropriate label for the latent trait we try to measure. A group of studies use the term, “coup-proofing effort,” and discuss how coup-proofing effort is influenced by coup-risk (Belkin and Schofer, Reference Belkin and Schofer2003, Reference Belkin and Schofer2005; Böhmelt and Pilster, Reference Böhmelt and Pilster2015; Sudduth, Reference Sudduth2017a, Reference Sudduth2017b). In our study, Θ_it, the value of the latent variable for country i and year t, is essentially a fixed parameter. The problem with categorizing coup-proofing as an effort is that it can lead to implicit theoretical assumptions about how theta arise. There is no definite consensus on how coup-proofing arises in the existing literature. Some studies suggest that leaders or regimes implement coup-proofing measures as the likelihood of a coup increases (Biddle and Zirkle, Reference Biddle and Zirkle1996; Quinlivan, Reference Quinlivan1999; Belkin and Schofer, Reference Belkin and Schofer2003; Thyne, Reference Thyne2010; Pilster and Böhmelt, Reference Pilster and Böhmelt2012), while others indicate that coup-proofing measures are more likely to be implemented as the likelihood of a coup decreases (Braithwaite and Sudduth, Reference Braithwaite and Sudduth2016; Sudduth, Reference Sudduth2017b). If we categorize coup-proofing as effort, there is a possibility of overinterpreting the strength of the empirical evidence by making unwarranted assumptions about the process through which Θ_it originates. Instead, we clarify our empirical contribution using the concept of the extent of coup-proofing, recognizing that we do not deduce the process through which Θ_it arises, but rather how relevant indicators relate to an unobserved trait, coup-proofing, as a fixed parameter.

Paine (Reference Paine2021) uses the term “strong coup-proofing institutions” to conceptualize the strength of coup-proofing. We might consider employing “institution” as a conceptual label for coup-proofing. The challenge lies in the fact that the term institution is conventionally utilized in the existing literature to denote individual security or military organizations.Footnote ¹ Labeling the unobservable latent trait as coup-proofing “institution” would not only cause confusion with existing research, but also fails to adequately capture the comprehensive nature of the latent trait. For example, security “institution” is one of the many manifestations of the unobservable latent trait we are trying to measure.

In what domains can the extent of coup-proofing be observed, which restricts the capacity of the military to execute successful coups? Numerous works have emphasized the significance of counterweights, such as security forces outside the military chain of command, that eliminate the military's capacity to plan and execute successful coups (Quinlivan, Reference Quinlivan1999; Belkin and Schofer, Reference Belkin and Schofer2005; Böhmelt and Pilster, Reference Böhmelt and Pilster2015; Thyne, Reference Thyne2017; Albrecht and Eibl, Reference Albrecht and Eibl2018; De Bruin, Reference De Bruin2018; Florea, Reference Florea2018; Mehrl and Choulis, Reference Mehrl and Choulis2021). Counterbalancing mechanisms play a crucial role in preventing coups by introducing obstacles that make it difficult for coup attempts to be coordinated. Counterbalancing makes it more difficult for high-ranking officials to organize a coup face-to-face (Singh, Reference Singh2014; Albrecht and Eibl, Reference Albrecht and Eibl2018). Detection or monitoring is an important factor that hinders coup plotters’ coordination. Bürkner (Reference Bürkner2017, Reference Bürkner2019) and De Bruin (Reference De Bruin2020b) elaborate on this point, explaining that presidential guards and paramilitary groups can proactively monitor and detect suspicious movements of the regular military, thereby preventing coup plotters from seizing important targets. Multiple internal security agencies with overlapping jurisdiction are able to continuously monitor the loyalty of the military with independent communication channels to leaders, preventing coup plotters from recruiting sympathizers and advancing their plans (Quinlivan, Reference Quinlivan1999: 133).

Even if a coup occurs, security forces outside the military chain of command are more likely to fight against it because they develop institutional interests distinct from the interests of the regular military (De Bruin, Reference De Bruin2020b: 133). Overall, an increase in the number of security forces serves as an indicator of the level of coup-proofing, which aims to reduce the military's ability to carry out a coup and raise the costs associated with executing a coup.

Security forces are required to directly control the violent aspects of the military's ability to stage a coup. The civilianization of cabinet posts is an important indicator that reflects the diminishing political influence of the military, serving as a safeguard against coups. This is based on the premise that militaries with greater political resources are more likely to effectively orchestrate a coup (Acemoglu et al., Reference Acemoglu, Ticchi and Vindigni2010; Svolik, Reference Svolik2012; Sudduth, Reference Sudduth2016). The “civilization” of the military's political power, as shown by the presence of civilian elites in cabinet positions, can increase the coup-proofing effects of the counterbalance. Civilianizing cabinet positions consolidate political leaders’ control over security forces and facilitates institutional reforms intended to counterbalance the military. Civilianizing cabinet positions can also increase the costs for the military to plot and carry out a coup because it increases non-military political support for a leader by allocating cabinet positions to civilian elites.

In particular, political leaders can fill interior and defense positions with civilian elites, such as their relatives and loyalists, rather than the military elite. The purpose of this measure is to ensure that security forces under the Ministry of Interior and Defense, such as regular armed forces and interior troops, are capable of preventing and putting down a coup. For example, armed forces such as the interior troops and the national police (the National Gendarmerie), which are normally commanded by the Minister of the Interior, played a crucial role in thwarting Lieutenant Kelly Ondo Obiang's 2019 coup attempt in Gabon. When uniformed politicians occupy these cabinet positions, there is a risk that they may favor and assist military intervention in politics or coup attempts (White, Reference White2017). Appointing civilian elites to non-security cabinet positions in the Ministry of Justice and Foreign Affairs is also crucial for judicial oversight and the prosecution of coup plans, as well as to prevent the military from exploiting its influence to seek foreign support from other countries (Barany, Reference Barany2019).

Appointment of civilian ministers to cabinet positions has been found to strengthen the support base of political leaders, as it serves as a mechanism for distributing patronage and improving the government's efficacy (Anene, Reference Anene1997; Kroeger, Reference Kroeger2020). The outcome of this strategy is that various ethnic groups and social factions within society are garnered as potential allies, thereby reinforcing the objective of thwarting military coups, as Huntington (Reference Huntington1957) similarly highlights in his analysis of subjective civilian control. Moreover, cabinets comprised of “non-military” civilian elites, such as relatives of political leaders and technocrats (Gandhi and Lawrence Sumner, Reference Gandhi and Lawrence Sumner2020), are less resistant to organizational reforms and counterbalances aimed at reducing the military's ability to stage a coup.

One could argue that the level of civilization found in these cabinets does not accurately reflect the extent of coup-proofing. This is because the level of civilization varies greatly across different regime types, but remains relatively consistent within the same regime type, such as a military regime. Even in military regimes such as those in Africa, however, a number of studies demonstrate a gradual civilianization of cabinet positions as a result of military leaders’ decision to reduce the likelihood of military coups (Anene, Reference Anene1997; Eizenga, Reference Eizenga2021).

It is also important to note that the extent of coup-proofing is not always manifested in dramatic changes such as the removal of military officers. Preventing the military from “penetrating” a particular cabinet post, regardless of whether it was previously held by a military officer or a civilian elite, can also be an important coup-proofing manifestation, as the military's influence in a number of areas, such as control of internal security forces, judicial control, and foreign affairs, ultimately increases its political power and coup-making capabilities. Obviously, it is difficult to ascertain the precise situation within the regime that could allow us to “observe” the continued civilianization of the cabinet. The fact that the military has not gained or regained control of key cabinet positions, however, can be considered the extent of coup-proofing.

Purges and decreases in military expenditure are also indicators of the extent of coup-proofing. By purging disloyal officers and heads of security organizations, leaders not only eliminate potential threats but also send a signal to potential coup plotters that they are capable of identifying them (Roessler, Reference Roessler2011; Braithwaite and Sudduth, Reference Braithwaite and Sudduth2016; Sudduth, Reference Sudduth2017b; Boutton, Reference Boutton2019). Several studies suggest that increasing military spending may reduce military resentment and their inclination to intervene in politics (Bove and Nisticò, Reference Bove and Nisticò2014; Leon, Reference Leon2014; Powell et al., Reference Powell, Faulkner, Dean and Romano2018). However, as Powell (Reference Powell2014) notes, expanding the military's size and political influence through an increase in defense spending may enhance their ability to carry out coups. As such, we should consider reducing military spending as a key component of the extent of coup-proofing. A substantial decrease in military spending would deprive potential coup plotters of resources, making it more difficult for them to overthrow the government.

Scholars place a greater emphasis on the application of a variety of coup-proofing measures, which include multiple aspects that collectively contribute to the coup-proofing strategy's effectiveness. De Bruin (Reference De Bruin2020a: 18) points out that different combinations of coup-proofing tactics could exist. Although the efficacy of coup-proofing is subject to debate, extant research reveals that political leaders typically employ a variety of such strategies (Quinlivan, Reference Quinlivan1999; Albrecht, Reference Albrecht2015b; Talmadge, Reference Talmadge2015; Reiter, Reference Reiter2020). The implementation of a civilianized cabinet could aid in the execution of measures that have the potential to trigger military retaliation, such as establishing counterbalancing security forces and conducting purges. Highly coup-proof regimes can show the simultaneous manifestation of multiple coup-proofing indicators, which indicates the regime's comprehensive coup-proofing.

It is crucial to identify which theoretically relevant variables manifest in the extent of coup-proofing. However, the existing literature lacks an adequate effort to establish a measurement for coup-proofing based on cross-national time data. Prior studies have employed a Bayesian item response method to gauge conceptually distinct constructs. While Gandhi and Lawrence Sumner (Reference Gandhi and Lawrence Sumner2020) concentrates on the consolidation of political leaders’ absolute power over elites, Kenwick (Reference Kenwick2020) focuses on civilian control, which refers to the degree of subordination of the military to civilian leadership. The measure of coup-proofing utilized in our study is distinct from measures of power consolidation and civilian control in terms of its underlying conceptual framework. Although the extent of coup-proofing may be a factor in a political leader's consolidation of power, it does not guarantee authority over all societal forces besides the military.

The concept of civilian control involves the subordination of the military across all policy domains of the state by the civilian leadership, while coup-proofing aims to decrease the likelihood of a military coup. Although these concepts are conceptually distinct, they are closely related in the context of civil–military relations. In terms of scope, civilian control is more comprehensive than coup-proofing (Brooks, Reference Brooks2019: 385). Kenwick (Reference Kenwick2020: 2) points out that coup-proofing and civilian control can be viewed as means and ends, respectively, and that their relationship is indeterminate. Therefore, he argues that it is essential to quantify coup-proofing using measurement modeling, specifically IRT, as he carried out in his study. In addition, he emphasizes the importance of investigating the causal effect of coup-proofing on civilian control (Kenwick, Reference Kenwick2020: appendix).

In our study, we can assess the conceptual distinctiveness of the constructs put forth in the works of Gandhi and Lawrence Sumner (Reference Gandhi and Lawrence Sumner2020) and Kenwick (Reference Kenwick2020) by comparing them with our own measure. While their model incorporates regime indicators and party types to gauge the consolidation of authoritarian power and civilian control on a broader level, our model focuses on different types of security forces to capture the extent of coup-proofing not accounted for in their work. To evaluate the construct validity of our measurement, we can determine whether and to what extent the two concepts listed above are related to ours.

2. Modeling coup-proofing

2.3 Items that identify the extent of coup-proofing

As previously discussed in the conceptualization section, various manifestations of coup-proofing can be observed across multiple domains. In this section, we describe the procedure and data employed to generate dichotomous items for the analysis of the two-parameter (2PL) IRT model. The first group of items corresponds to the presence of security forces, such as presidential guards and paramilitary organizations, to counterbalance the military with other security forces. The second group of items refers to the presence of civilian elites in various cabinet positions, which can reduce the military's coup-making capacity and increase the cost of a coup. A purge item denotes the elimination of disloyal military officers. Lastly, the reduction in the defense spending indicates a decrease in the material capabilities of the military.

Security forces are recording the existence of additional security forces beyond the traditional military forces of the army, navy, and air force, and whether these forces serve as a “counterweight” to the military. To construct our measures, we use De Bruin's State Security Forces Dataset (SSFD), which includes 375 security forces in 110 countries from 1960 to 2010 (De Bruin, Reference De Bruin2019). Previous studies have included regular forces, such as army and marine corps troops, to devise measures of counterbalancing (Belkin and Schofer, Reference Belkin and Schofer2005; Pilster and Böhmelt, Reference Pilster and Böhmelt2011). However, scholars have raised concerns about the consistency and accuracy of the cross-national data on counterbalancing, which relies on the International Institute for Strategic Studies’ Military Balance (Colgan, Reference Colgan2011; De Bruin, Reference De Bruin2019). In contrast, the SSFD provides more precise measures of security forces and counterbalancing because it uses consistent inclusion criteria. Moreover, the SSFD data provide comprehensive information on various security forces, including those that exist outside the regular military chain of command.

We consider two conceptual dimensions using indicators from the SSFD data. First, the creation of a coercive apparatus to counterbalance the military can be evaluated based on the presence of a variety of security forces outside the regular armed forces. Second, the functional features of security forces are related to the central idea behind coup-proofing. As Quinlivan argues, coup-proofing is “to prevent troops from moving on the centers of the regime, and a task is best accomplished by a ground-based parallel military (Quinlivan, Reference Quinlivan1999: 142).” If security forces are stationed near the capital and operate outside the regular military chain of command, they can serve as effective counterweights to a coup d’état. To capture the variety of security forces, we use dichotomous indicators of security forces, such as the presidential guard, secret police, militarized police, interior troops, militia, and border guards from the SSFD data. These indicators take the value of 1 if one or more of each security force exists and 0 otherwise.

The IRT model used in our study includes two dichotomous indicators from the SSFD data sets, namely Military unit independent and Military counterweight present, in addition to indicators of different types of security forces. The indicator Military unit independent is coded as 1 if there exists more than one military unit that reports to the regime through at least one supervising body distinct from that of the regular military, and 0 otherwise. Similarly, the indicator Military counterweight present is coded as 1 if there exists more than one military unit stationed within 60 miles of the capital outside the regular military chain of command, and 0 otherwise.

The presence of civilian elites in cabinet positions indicates whether non-military civilian elites hold different cabinet positions. To determine this, we use the Military Participation in Government data compiled by White (Reference White2017). The data enable us to identify whether defense, interior, justice, and foreign affairs positions are occupied by non-military civilian elites or active-duty military officers. Additionally, we identify whether civilian elites hold security-related or non-security-related cabinet positions outside these four areas. Dichotomous indicators have a value of 1 when non-military civilian elites occupy these cabinet positions, and a value of 0 when active-duty military officers hold them. This allows us to track changes in cabinet positions from civilian elites to military officers and vice versa.

A purge of military officers is a case in which a leader demotes and discharges military officers from key positions. A political leader uses this method not just to directly replace dishonest military members with loyalists but also to send a signal to potential coup plotters. The Military Purges in Dictatorships (MPD) data focus on individuals who have legitimate access to physical forces capable of violence (Sudduth, Reference Sudduth2020). While the Banks Cross-National Time Series Data Archive also provides information about purges (Banks and Wilson, Reference Banks and Wilson2021), it includes the purges of civilian elites. Since our study focuses more on coup-proofing strategy limited to the military, the MPD data are more appropriate for our conceptualization. Military purge takes the value 1 in a year when one or more military purges occur and 0 otherwise.

Defense budget reduction is a material aspect of coup-proofing. By allocating fewer resources to the military, a regime can limit the military's material capability (Acemoglu et al., Reference Acemoglu, Ticchi and Vindigni2010; Powell, Reference Powell2014; Powell et al., Reference Powell, Faulkner, Dean and Romano2018). The National Material Capabilities data version 5.0 provides information about each state's total military budget for each year from 1816 to 2012 (Singer et al., Reference Singer, Bremer and Stuckey1972). Reductions in the defense budget may indicate a decline in the material capability of the military, but they may also be the result of external shocks unrelated to coup-proofing (e.g., the end of a war). Obviously, we cannot identify all factors that influence the reduction in military spending, but by excluding cases occurring up to three years after the end of an interstate war, we can remove the external factor that clearly influences the reduction. We utilize the Correlates of War (COW) data on interstate wars to determine when a war begins and ends (Maoz et al., Reference Maoz, Johnson, Kaplan, Ogunkoya and Shreve2019). To ascertain the decrease in military spending, we compare each year's military spending to the average of the previous three years. Except for cases occurring up to three years after the end of an interstate war, a decrease in military spending is coded as 1, while an increase or consistency is coded as 0.

The first column of Table 1 provides a summary of the items that are designed to measure the extent of coup-proofing. The second column indicates an upward arrow if the item is expected to increase the level of coup-proofing in the given country-year.

Table 1. Indicators of the extent of coup-proofing

2.4 IRT model specification

We estimate the extent of coup-proofing in 2947 country-years between 1965 and 2005 by analyzing 76 nations using the country-year as the unit of analysis. We utilize various items that are relevant to different dimensions of coup-proofing, as mentioned in the preceding section. We use a 2PL IRT model that can be fitted using the R package, brms. The 2PL model evaluates levels of coup-proofing by examining observable manifestations, which take the following mathematical form:

(1)$${Pr}( {Y}_{itj} = 1\vert \Theta_{it},\; \beta_{\,j},\; \alpha_{\,j}) = {{\rm exp}[ \alpha_{\,j}( \Theta_{it} + \beta_{\,j} ) ] \over 1 + {\rm exp}[ \alpha_{\,j}( \Theta_{it} + \beta_{\,j} ) ] }$$

where Pr(Y _itj = 1) is a probability that takes the value 1 if item j is observed in country i in year t and 0 otherwise. For example, if a purge of military officers or a paramilitary force is observed in country i in year t, this indicator takes the value of 1; otherwise, it is 0. If a civilian elite holds the position of Minister of the Interior or Minister of Defense, the value will be 1, whereas the value will be 0 if the position is held by a military officer. We can therefore interpret Θ_it as the latent extent of coup-proofing in country i at time t. A higher Θ_it indicates a greater level of coup-proofing.

Each item has two parameters: the item easiness parameter β _j and the item discrimination parameter α _j. We can interpret β _j as the easiness of item j, as a higher β _j implies a higher probability of correctly answering a given latent variable. When β _j is large and positive, it indicates that the item is easier to implement.Footnote ⁴ The other parameter, α _j, determines how well the items discriminate between regimes across different levels of coup-proofing. An item is better able to discriminate between regimes as α _j increases. In a 2PL model, we assume that α _j is positive for all items, which is a reasonable assumption for our data set in which a y = 1 always indicates coup-proofing.Footnote ⁵

To conduct IRT modeling, we rely on the R package brms which allows for Bayesian estimation in Stan using MCMC sampling via adaptive Hamiltonian Monte Carlo (Hoffman and Gelman, Reference Hoffman and Gelman2014; Bürkner, Reference Bürkner2019; Bürkner and Vuorre, Reference Bürkner and Vuorre2019). brms enables us to predict the parameters of interest using the distributional regression framework (Bürkner, Reference Bürkner2017, Reference Bürkner2020). We place a normal prior on Θ_it, which represents the latent trait, such that Θ_it ~ N(0,  1).Footnote ⁶

Additionally, we use a normal prior β _j ~ N (0, 10) as an easiness parameter to constrain β _j to a reasonable range of values to avoid having the posterior distribution excessively influenced by the prior. To force α _j to be positive, we assign the weakly informative prior α _j ~ Gamma(4, 3), assuming that all items contribute to the latent variable in the same direction.Footnote ⁷

3. IRT estimation results

The extent of coup-proofing in 76 countries from 1965 to 2005 is estimated.Footnote ⁸ The 2PL IRT model generates posterior distributions for three parameters: discrimination, easiness, and latent levels of coup-proofing across countries and time.

To interpret the results of the Bayesian IRT model, it is crucial to assess whether the model achieves convergence. The $\hat {R}$ convergence diagnostic compares the between- and within-chain estimates for model parameters and other univariate quantities of interest. If the chains do not mix well, $\hat {R}$ exceeds 1. All $\hat {R}$ values in our IRT models are less than 1.01 (refer to Figure 3 in the Appendix), indicating conformity with conventional criteria. Bulk-ESS refers to the effective sample size based on the rank-normalized draws. A higher Bulk-ESS implies better performance, conventionally requiring at least 100 times the number of chains. For instance, if four chains are running, the rank-normalized effectiveness should be at least 400. In our IRT model, most parameters have a Bulk-ESS higher than 400. MCMC chains converge to the same target distribution if they mix well individually (i.e., quickly jumping up and down) and overlay one another simultaneously. A graphical summary of the marginal posterior densities and the MCMC chains indicates that the chains are well-mixed individually (refer to Figure 4 in the Appendix).

Figure 1 presents posterior estimates of the easiness and discrimination features of the coup-proofing indicators (items). In panel (a), we observe that establishing a militarized police is easier than establishing a presidential guard or secret police. Substantively, if we want to witness a presidential guard and secret police, the regime needs to be highly coup-proofed. In contrast, we observe a militarized police even in regimes with a low level of coup-proofing.

Figure 1. Estimates of easiness (a) and discrimination (b) parameters for each of the 16 indicators in the IRT model. Dots represent means of posterior distribution, and bands represent 2.5–97.5 percent highest posterior density credible intervals.

The easiness parameters for military counterweight and military independent are both quite low, indicating that we can observe the formation and maintenance of these security organizations only when a regime has a very high degree of coup-proofing. These patterns of security organization easiness parameters align with the well-known idea that constructing security organizations that directly counterbalance the military is difficult (Sudduth, Reference Sudduth2017a).

As for the civilianization of the military in cabinet posts, we find that civilian foreign affairs and civilian justice have higher easiness of parameter values than civilian interior and civilian defense. This suggests that a regime needs to be more coup-proofed than others show civilianization of cabinet positions which influence the use of force. In contrast, the civilianization of cabinet positions, which has little effect on the use of force, does not necessitate a high level of coup-proofing to manifest.

In panel B of Figure 1, we observe how well each item discriminates across degrees of coup-proofing. A large discriminating parameter estimation value for a given item indicates effective differentiation between country-years with high and low levels of coup-proofing. Notably, the military counterweight and military independent items exhibit the highest estimation values among the security forces items, corresponding to the lowest easiness parameter values. Similarly, the military counterbalance and military independent items show the highest estimation values among the security organization items, also corresponding to the lowest easiness parameter values. These findings suggest that military counterbalance and military independent are hard to implement, but they effectively differentiate the extent of coup-proofing across observations.

Several characteristics of the estimated discrimination parameter values are worthy of consideration. We observe that the discrimination parameter values for civilian foreign affairs and civilian justice are quite high despite their easiness parameter values being very high. This suggests that these two items distinguish between regimes with a low level of coup-proofing and those with a moderate level, but not a high level.

Also, the discrimination parameter values for civilian defense and civilian security position are small relative to those of civilian non-security position and civilian interior. Civilian oversight of defense and security positions should be able to distinguish a regime's degree of coup-proofing more effectively than oversight of non-security positions, as we think security-related positions are more crucial to coup-proofing. As stated in the previous section, however, our IRT model does not rely on theoretical assumptions regarding the relative importance of items; instead, item weights are determined as part of the estimation process.

Based on these estimated results, we can infer that control over the interior ministry is just as important for preventing coups as control over the defense and security forces. Regimes utilize the interior troops or national gendarmerie to suppress a coup, although not all ministries of the interior have armed forces. Due to their geographical proximity and more rapid access to internal coup plots, these armed groups affiliated with the interior ministry may be more effective at preventing coups than traditional military forces. Therefore, civilian oversight of an interior ministry can be an important coup-proofing factor, which may explain the unexpectedly large value of the discrimination parameter.

The values of the discriminant parameters can also differ depending on the inclusion or exclusion of an item. Considering the exploratory nature of our modeling on the extent of coup-proofing, we can observe how the pattern of estimation results differs when we exclude items associated with non-security cabinet positions. Figure 1 in the Appendix displays the posterior estimates of the easiness and discrimination parameters for the coup-proofing indicators (items). The estimates are presented after excluding the indicators for civilian non-security position, civilian foreign affairs, and civilian justice. The easiness parameter values do not change relative to the pattern of estimation results shown in Figure 1 of the main text. However, the discrimination parameter values for civilian interior and civilian security position become smaller than the value of civilian defense. Despite the fact that these results are consistent with the conventional notion that civilian oversight of the defense cabinet is essential, what constitutes a “good” item and how item selection should occur depends on a variety of factors, such as content validity and item clarity. Our exploratory approach to item selection has the potential to facilitate the development of future coup-proofing models that are more consistent with the researcher's theoretical objectives.Footnote ⁹

The IRT model's posterior estimate of coup-proofing levels, denoted as θ, is our primary interest. We display the posterior mean estimate distributions for all 2947 country-years between 1965 and 2005 in Figure 2, with a mean estimate of −0.002 and a range of −1.79 to 1.89. Figure 3 highlights interesting patterns in the differences of mean distributions for various authoritarian regimes.Footnote ¹⁰ When comparing single-party (b) and personalist regimes (c) to military regimes (a), we observe that military regimes exhibit the lowest average level of coup-proofing. This result is consistent with the conventional wisdom that military regimes do not actively work to reduce their military's capability to stage coups.

Figure 2. Distributions of latent measures of the level of coup-proofing.

Figure 3. Distributions of latent measures of the level of coup-proofing depending on the different types of authoritarian regimes (static IRT model): (a) military regimes (412 country-years), (b) party regimes (981 country-years), (c) personal regimes (447 country-years), and (d) monarchy regimes (232 country-years).

It is also interesting to compare estimated distributions to empirical findings from previous studies on the relationship between counterbalancing and authoritarian regimes. Escribà-Folch et al. (Reference Escribà-Folch, Böhmelt and Pilster2020) discovered that counterbalancing mechanisms are more common in personalist regimes than in single-party and military regimes. Our study finds that personalist regimes (c) exhibit a higher level of coup-proofing than military regimes (a), but a lower level of coup-proofing compared to party regimes (b). It is important to note that our primary objective is to measure the overall level of coup-proofing, not a single coup-proofing mechanism.Footnote ¹¹ Finally, we find that monarchies (d) have the highest level of coup-proofing among authoritarian regimes. This finding suggests that monarchies are more likely than other authoritarian regimes to reduce the military's coup-making capability and increase coup costs (Gandhi and Lawrence Sumner, Reference Gandhi and Lawrence Sumner2020).

By comparing mean estimates over time for two countries, we can improve our understanding of how our estimates correspond to real-world situations. Figure 4 illustrates the variation in estimates of the extent of coup-proofing over time for Pakistan (a) and Mexico (b). The figure shows that not only do our estimates vary within a single country but also that cross-national differences exist. Panel (a) of Figure 4 shows that the era of civilian leaders, such as Zulfikar Ali Bhutto and Benazir Bhutto, had far higher levels of coup-proofing than the era of military leaders, such as Muhammad Zia-ul-Haq and Pervez Musharraf. This pattern is consistent with our earlier finding that military regimes have a lower level than democracies and other types of authoritarian regimes. Additionally, the estimates also vary over the course of a leader's tenure in power, as seen with Zulfikar Ali Bhutto, Muhammad Zia-ul-Haq, and Pervez Musharraf.

Figure 4. Levels of coup-proofing in (a) Pakistan and (b) Mexico between 1965 and 2005. The mean posterior estimates of coup-proofing are indicated by a solid line. The bands around the solid line represent 95 percent credible intervals.

In Pakistan, Benazir Bhutto attempted to reduce the military's capability following her party's election victory in 1988 by removing military personnel from the intelligence agency and her cabinet (Shafqat, Reference Shafqat1997). Despite the fact that Bhutto and her civilian successor, Nawaz Sharif, frequently compromised with the military throughout the 1990s, the estimation results reveal their decisions to tighten their grip on the military.

In contrast to Pakistan, where coup-proofing levels fluctuate drastically, Mexico's levels are relatively stable, with the exception of two presidents, Carlos Salinas and Vicente Fox. This consistency aligns with Mexico's historically stable civil–military relations, which have been dominated by the Institutional Revolutionary Party (Díez, Reference Díez2012). Pakistan's extremely volatile coup-proofing levels contrast starkly with Mexico's relatively low coup-proofing levels.

3.1 Construct validity of coup-proofing measurement

Construct validity refers to the extent to which a measure accurately assesses what it is supposed to measure. When assessing something that cannot be measured or observed directly, it is important to examine construct validity. Examining discriminant validity helps establish construct validity by demonstrating that two concepts that should not be related are, in fact, not related (Grant and Kelly, Reference Grant and Kelly2008). Determining discriminant validity involves examining the degree of correlation between coup-proofing and civilian control and consolidation of power. Furthermore, we can assess construct validity by examining whether our operationalization of a concept yields plausible and interesting results in light of a preexisting hypothesis (Adcock and Collier, Reference Adcock and Collier2001). If our measurement of coup-proofing has construct validity, we should observe a consistent negative effect on both the attempt and success of a military coup.

Figures 5 and 6 show that our measure of extent of coup-proofing and Kenwick's measure of civilian control have a moderate correlation, with a Pearson's r value of 0.541. A moderate association between measures in the range of 0.40–0.60 can indicate that the measures being examined are valid measures of different but related concepts. This finding supports Kenwick's speculative argument that coup-proofing and civilian control are distinct but related concepts. Pearson's r value for the comparison with power consolidation, on the other hand, is a very low 0.093, indicating a higher discriminant validity. This demonstrates that coup-proofing and power consolidation are measuring completely different concepts.

Figure 5. Correlations between coup-proofing and civilian control and power consolidation.

Figure 6. Coup-proofing, civilian control, and consolidation of power.

It is important to demonstrate that, despite their correlation, the two measures of civilian control and coup-proofing do not produce the same scores. To achieve this goal, we conduct a comparative analysis of how the levels of civilian control and coup-proofing change over time within the same country. Using a static IRT model, we illustrate in Figure 7 the respective posterior estimates of the extent of coup-proofing and civilian control over time in Guatemala. Between 1965 and 1985, a lengthy military regime governed Guatemala. Although Vinicio Cerezo's civilian leadership was established following the 1986 election held under the new constitution, the military continued to wield political influence behind the scenes until 1996, when the 36-year civil war between the government and the guerrilla ended.

Figure 7. Coup-proofing and civilian control (Guatemala).

In Figure 7, the extent of coup-proofing is highly correlated with civilian control, but it also vary over time. For instance, between 1970 and 1982, the extent of coup-proofing fluctuated significantly, whereas civilian control was relatively stable. In contrast, levels of civilian control plummeted overtime after 1990, while the extent of coup-proofing remained largely unchanged. As Kenwick noted, additional theoretical analysis and empirical investigation will be required in future research to fully comprehend the indeterminate relationship between civilian control and coup-proofing.

We also assess construct validity by determining whether our operationalization of a concept yields plausible and interesting results. If the objective of coup-proofing is to reduce the military's capability, then counterbalancing, a key component of coup-proofing, should have negative effects on both coup attempts and coup success, according to the conventional wisdom. Nonetheless, as demonstrated by a number of studies, counterbalancing has inconsistent effects on military coup attempts and success (Powell, Reference Powell2012; Böhmelt and Pilster, Reference Böhmelt and Pilster2015; De Bruin, Reference De Bruin2018, Reference De Bruin2020a, Reference De Bruin2020b). If our measurement of the extent of coup-proofing has reasonable construct validity, we can observe a consistent negative impact on the attempt and success of a military coup.

We conduct a logit analysis to test the effects of our measure of coup-proofing, with coup attempt and coup success as dependent variables and coup-proofing as the independent variable. Fixed effects in a logit model lead to a significant number of observations (about 40 percent) being dropped from our analysis. Thus, it is also possible to estimate linear probability models using ordinary least squares with and without country-fixed effects to determine how much cross-country versus within-country comparisons influence estimation results.

We utilize data on global coups from Powell and Thyne (Reference Powell and Thyne2011), which distinguishes between coup attempts and successful coups. To adjust for temporal dependence, we use the number of years that elapsed between coup attempts in a country, as well as its square and cube, in our models (Carter and Signorino, Reference Carter and Signorino2010). At the country level, we apply cluster-robust standard errors to ensure consistent standard errors. Table 2 presents the estimation results, which demonstrate that our coup-proofing measures have negative effects on coup attempts and coup success. Both the Linear Probability Model (LPM) with fixed effects and the LPM model without fixed effects yields coefficients that are statistically significant. It indicates that the effect of coup-proofing on military coups varies not only across countries but also within each country. When including two additional control variables, such as democracy and per capita GDP, we find that the negative and statistically significant effects of coup-proofing persist only for military coup attempts, as shown in Table 2 of the Appendix.

Table 2. Effects of coup-proofing on military coups, 1965–2005

Notes: Robust standard errors are in parentheses.

Controls for time dependence are included but not shown.

*p < 0.10, **p < 0.05, ***p < 0.01.

Overall, the distribution of our coup-proofing measurement is consistent with conventional wisdom. In addition, we demonstrate the construct validity of our measurement by comparing its divergent validity to measures of civilian control and consolidation of power. We also demonstrate additional construct validity by proving that the extent of coup-proofing negatively impacts coup attempts and success.