Naturalisation in context: how nationality laws and procedures shape immigrants’ interest and ability to acquire nationality in six European countries

This article focuses on the interest and ability to acquire destination country nationality among non-EU-born adults in six European countries. While a sizeable literature has emerged on nationality policies and acquisition rates among immigrants, the ways that policies affect the acquisition process are less well understood. A key question is how laws and procedures affect the interest of immigrants to acquire nationality and their ability to do so in practice. This article argues that both immigrants’ interest and ability to acquire nationality are largely driven by their context, but in very different ways, depending on their individual, origin and destination country characteristics. The analysis finds that interest to acquire nationality is particularly affected by origin country dual nationality laws and destination country nationality procedures, while destination country nationality laws and procedures are the major determinant of immigrants’ ability to acquire nationality. These findings give citizenship policymakers reason to reflect on the potential impact of their laws and procedures on ability and interest, particularly given the fact that promotional measures and targeted integration support are generally weak across Europe.


Introduction
While nationality policies are a key indicator of a country's overall approach to immigrant integration (Huddleston and Vink 2015), nationality acquisition rates remain low and divergent among settled immigrants across Europe (OECD/EU 2018). The average in the EU is 59% compared to 62% in the United States, 81% in Australia and 90% in Canada.
Policymakers and scholars often point at differences in nationality laws and immigrant populations in order to explain these differences in nationality acquisition across countries (Brubaker 1992;Joppke 2007;Goodman 2010). Debates on nationality acquisition predominantly focus on the well-researched reasons and the laws for nationality acquisition, with most attention to the legal requirements for ordinary naturalisation.
Yet an "implementation gap" appears to emerge across Europe when reviewing nationality laws, nationality procedures and uptake of nationality acquisition. Firstly, no systematic correlation emerges in Europe between the restrictiveness of ordinary naturalisation laws and procedures (Huddleston 2013). Looking at 35 European countries, half of the countries have laws and procedures with different degrees of restrictiveness: 9 countries facilitate both the law and procedure (e.g. Portugal and Sweden) 9 countries restrict both the law and procdure (e.g. Hungary and Italy) 4 countries restrict both the law and procedure (e.g. Baltics and to some extent France and Germany) 13 countries facilitate the law but restrict the procedure (e.g. Belgium, Ireland and Spain) In other words, looking only at the legal requirements does not indicate what or how many obstacles exist in the procedure.
Secondly, the correlation between nationality laws and acquisition rates is positive but weak. Settled immigrants from developing countries seem more likely to acquire nationality in some countries with restrictive laws than in others with similar or even more inclusive laws (see Huddleston and Falcke 2020). Most analyses study the end of the nationality acquisition process (i.e. the rate or share of nationality acquisition), but not the entire process of implementation which include distinct steps whereby immigrants become interested in nationality, apply for nationality acquisition and persevere until they succeed.
One explanation for the uneven relationship between nationality laws and acquisition rates across Europe could be that the 'rules in the books' leave a lot of space for 'rules in practice' and 'discretion' in action. Nationality laws are the substantive requirements that determine the eligibility and criteria for nationality acquisition or loss, while procedures are each of the formal steps or stages in the process of implementing these criteria. The implementation of nationality laws creates specific opportunities and obstacles at all steps in the procedure. For immigrant adults, applying for nationality is a subjective choice that can be either encouraged or discouraged within their context. For authorities, naturalisation is rarely an automatic process decided by one decisionmaker based on entirely objective requirements. The main aim of this article is to explore how differences in naturalisation procedures affect nationality acquisition and relate to the different major steps in the process for immigrant adults in Europe. This paper undertakes the first cross-national analysis of immigrants' interest and ability to acquire nationality. This paper assesses the links between nationality laws and procedures, on the one hand, and the interest and ability for nationality acquisition among non-EU-born adults in six European countries. This scope focuses on the groups most likely to acquire nationality, on the one hand, and a diversity of destination countries and nationality laws and prcoedures, on the other. The paper's analytical framework and hypotheses are underpinned by a review of two major gaps in the citizenship literature: the importance of contextual factors and the difference between immigrants' interest versus ability to acquire nationality. The methodological section assesses the strengths and weaknesses of the paper's data source, the Immigrant Citizens Survey (Huddleston and Dag Tjaden 2012). Logistic regressions analyse the significance of nationality laws and procedures, alongside key individual-level and origin country factors. Several robustness checks are run with different types of regression analysis and different operationalisations of the main variables of interest. The paper concludes with a discussion of the findings in light of previous single-country studies and the main implications for researchers and policymakers.

Major determinants of nationality acquisition
The well-worn study of micro-level explanations of nationality acquisition started in North America (Bernard 1936;Evans 1988;Yang 1994;Devoretz 2008) and expanded to other traditional destination countries and Europe (see overview in Liebig and Von Haaren 2011). This extensive transatlantic literature has confirmed the importance of key individual, origin and destination country determinants of nationality acquisition. Immigrants' human capital, especially country-specific capital such as language proficiency, education, employment experience and residence duration, is usually presented as the major determinant of their 'civic capital' including nationality acquisition (Bernard 1936;Evans 1988;Yang 1994;Devoretz 2008;Liebig and Von Haaren 2011;Peters et al. 2018). Apart from human capital, social capital and networks help to shape the information and mobilisation channels that immigrants often need for nationality acquisition (Bloemraad 2006a;Just and Anderson 2012;Logan et al. 2012;Abascal 2015). Moreover, social capital reshapes the incentives for nationality acquisition. For immigrants with spouses or children, nationality acquisition is less of an individual choice than a collective choice to extend the benefits of nationality at negligible additional costs (Portes and Curtis 1987;Ivlevs and King 2012;Street 2014;Peters et al. 2016).
Increasingly, origin country characteristics are also included in multivariate analysis in order to reveal the significant range of relative benefits and costs for immigrants with different return migration prospects, based on their origin country's level of development, geographical distance, refugee flows and origin nationality policies (Portes and Curtis, 1987;Yang 1994;Jones-Correa 2001;Bueker 2005;Constant et al. 2007;Mazzolari 2009;Logan et al. 2012;Vink et al. 2013).
In addition to origin country characteristics, destination country characteristics are emerging as some of-if not the most-significant determinants of nationality acquisition. Building on American studies of policy changes (Jones-Correa 2001;Bloemraad 2006b;Haney-Lopez 2006;van Hook et al. 2006;Logan et al. 2012;Fox and Bloemraad, 2015), comparative research in Europe has contributed the most to the study of the links between acquisition rates and nationality policies, usually measured in terms of the legal requirements (Janoski 2010;Reichel 2011;Gonzalez-Ferrer and Morales 2013;Vink et al. 2013;Beine et al. 2016;Stadlmair 2017;Hansen and Clemens 2018).

Immigrants' interests: a hidden force behind the nationality acquisition process
While the literature has well-studied the overall factors driving nationality acquisition, little is known about how each factor influences each step in the process. Most studies of acquisition rates have difficulty disentangling interest and ability, due to data limitations and limited reflection on the entire nationality acquisition processes. Without this framework or data, factors found to be associated with nationality acquisition are either interpreted as associated with expected benefits (i.e. interest), expected costs (i.e. ability) or both. These difficulties with interpretation are outlined in the following analytical framework section under individual-level characteristics.
Disentangling interest from ability seems essential as the few single-country studies that do find that the key factors underlying nationality acquisition are associated in different and sometimes opposing ways with interest than with ability. These studies focus on a variety of anomalous cases, where immigrant groups have high expected returns on nationality acquisition, but low acquisition rates in practice. Acquisition rates have been lower-than-expected in the United States among Mexicans (Portes and Curtis 1987), in Germany after the 1999 Nationality law reform (Constant et al. 2007;Kahanec and Serkan Tosun 2009;Hochman 2011), in Latvia among the Russophone minority (Ivlevs and King 2012) and in France among immigrants with Muslim and disadvantaged backgrounds (Carrillo 2015). The factors predicting interest are fewer and rarely the same as for actual naturalisation (Portes and Curtis 1987). Uninterested immigrants are substantially different in profile and experience than interested and/or naturalised immigrants (Kahanec and Serkan Tosun 2009;Hochman 2011). The traditional individual-level factors associated with acquisition rates can explain ability to acquire nationality, but often not interest. That means overall acquisition rates do not reflect the full extent to which immigrants are interested to acquire nationality.
These studies suggest that interest in nationality may be driven less by ability and more by their context. Hochman (2011) places interest in nationality within a broader process of social identity formation among immigrants.
The factors reshaping immigrants' interpretation of the meaning of nationality were first identified by Portes and Curtis (1987) and expanded upon in later studies. The first two explanations are based on immigrants' relative benefits and social networks. The first explanation is immigrants' rootedness in the destination vs. origin country. Immigrants' return plans and incentives help to shape their identification with their destination country and their appreciation of the relative benefits and costs of nationality acquisition. The second explanation-'place of settlement' in the destination vs. origin country-fits with social capital theory as immigrants' family, friends and community may change their return plans and their appreciation of the benefits and meaning of nationality acquisition.
Nationality procedures: a second hidden force behind nationality acquisition Lastly, the 'informal characteristics' of the destination country (Hochman 2011) create specific 'barriers and attitudes' (Portes and Curtis 1987) that influence immigrants' awareness and attitudes about nationality acquisition. Immigrants with negative outgroup experiences may believe that nationality acquisition will not be able to deliver on the promised benefits or in-group acceptance (Kahanec and Serkan Tosun 2009;Carrillo 2015) All of the studies suggest that nationality laws and procedures can increase the psychological and practical obstacles to nationality acquisition.
The importance of nationality procedures are often 'hidden' from the view of researchers and policymakers who tend to focus on the legal requirements and on the immigrants who are interested and applied for nationality acquisition. Newfound attention to nationality procedures can be credited to the groundbreaking work of Irene Bloemraad. Building on North (1985) and Yang's (1994) catalogue of often-overlooked procedural obstacles, Bloemraad (2002Bloemraad ( , 2006a and later Aptekar (2016) identify significant qualitative differences in American and Canadian practices, particularly in terms of support and promotion. Bloemraad argues that, both before and during the procedure, bureaucracies and service-providers create a 'context of reception' and 'interconnected institutional con uration' that provide immigrants with significant symbolic or interpretative resources (i.e. to understand their benefits and interest in acquiring nationality) and material resources (i.e. to meet the costs). Since then, scholars have been inspired to measure the importance of specific promotional measures and practical obstacles like fees (Felix et al. 2008;Thränhardt 2008;Logan et al. 2012;Hainmueller and Hangartner 2013;Hainmueller et al. 2018). Nationality procedures are therefore an under-explored potential factor behind immigrants' interpretation of the meaning, benefits and costs of nationality.

Ability vs. interest to acquire nationality
Interest to acquire nationality can be defined as an immigrant's perception of the desirability of a formal membership and identification with the destination country. Nationality acquisition forms part of immigrants' intended life plan and migration trajectory. This intention can arise at any point in an immigrants' life.
The ability to acquire nationality can be defined as an immigrant's successful completion of the nationality acquisition process. Firstly, interested immigrants must be willing, eligible and able to submit their application. As the requirements in law are often subjective and discretionary, applicants must next pass through a decisionmaking process. In the end, authorities may not be willing or able to grant a positive decision, leading to either a delay or rejection.

Nationality laws and procedures
Destination country nationality laws are expected to have a positive relationship with interest and ability to acquire nationality (Vink et al. 2013), but a weaker relationship with interest than ability. Laws are expected to impact immigrants' ability to meet the requirements andto a lesser extentexert a certain signaling function affecting their interpretation of the meaning, benefits and costs of nationality acquisition.
H1: Inclusive nationality laws are positively associated with both immigrants' interest and ability to acquire nationality, but more strongly associated with ability than interest.
Building on Bloemraad (2002Bloemraad ( , 2006a, nationality procedures are expected to create the context and lived reality for nationality acquisition. Whether or not immigrants apply and succeed may depend on the availability of information and courses, the costs and the types of documentation and assessments required. The amount of discretion, bureaucracy and judicial review may also play a role in the procedure. The link with interest may be even greater for nationality procedures. Immigrants' attitudes are expected to be largely shaped by the support, treatment and information that they receive on the ground. Within nationality procedures, 'front-end' practices regulating access are expected to have greater significance than 'back-end' difficulties in the procedure. Promotion measures and documentation requirements can be described as the 'front-end' of the bureaucracy most visible and impactful for immigrants. These symbolic and material resources "help with the practicalities of participatory citizenship and cement feelings of inclusion and attachment to the country" (Bloemraad 2006a 237). The 'back-end' of the procedure, namely the discretion, bureaucracy and judicial review in decision-making, may only affect the pace and predictability of the procedure once immigrants apply. While promotion and documentation affect all potential applicants, the difficulties within the procedure may only lead to rejections and delays for a smaller share of applicants (see discussion in Helbling et al. 2011), without any major effect on interest or application rates.
H2: Inclusive nationality procedures are positively associated with both immigrants' interest and ability to acquire nationality, and more strongly associated with interest than ability.

Individual level characteristics
The available literature is not always clear on the expected link between immigrants' characteristics and their interest versus ability to acquire nationality.
Human capital can be expected to be positively associated with ability and, to some extent, interest. The literature is mixed on the link between education and interest. Both high and low-educated may see nationality as a signal to the receiving society in hopes of greater opportunity and investment in return. The literature is clearer about the link between human capital and ability. Human capital certainly increases immigrants' abilities. The process itself also often requires, whether formally and informally, that applicants have country-specific skills to interact autonomously with authorities and overcome obstacles in their way.
H3a: Human capital is positively associated with the ability and interest to acquire destination country nationality and more strongly with ability than with interest.
Socio-political capital is regularly associated in the literature with both interest and ability. Immigrants with effective family, community and political links may perceive a high cost for return migration and/or a strong interest in nationality as a means to political mobilisation, family unity and intergenerational social mobility (Ersanilli and Koopmans 2011;Just and Anderson 2012;Street 2014;Aptekar 2016). Socio-political capital may also facilitate ability to the extent that immigrants with these effective links have greater information, support and connections to succeed (Logan et al. 2012;Abascal 2015) H3b: Socio-political capital is positively associated with interest and ability to acquire nationality and more strongly with interest than ability.

Origin country dual nationality
Whether or not immigrants are allowed to retain their nationality enters into their cost/benefit analysis. Either its loss represents an insurmountable cost. Or its retention is a major portable benefit that can facilitate circular migration. The opportunity for dual nationality may have even influenced their decision to move to the destination country (Alarian and Goodman 2017). Going further, the opportunity for dual nationality fundamentally changes immigrants' cost/benefit analysis and the meaning of nationality itself, since renunciation is the only way that nationality acquisition creates a loss and, arguably, a lack of free choice (Yang 1994;Pantoja et al. 2001).
H4: Origin country tolerance of dual nationality is strongly associated with interest but not ability to acquire nationality.

Data and methodology
Data This analysis focuses on EU countries-the main laboratory for integration and nationality policy comparison within a supranational legal framework-and on non-EU citizens-the main subjects of integration policies and the populations most likely to acquire nationality. The analysis takes advantage of a specific survey of immigrants' needs and experiences of integration and nationality policies-the Immigrant Citizens Survey [ICS]. The survey was conducted from October 2011 to January 2012 among non-EU-born (i.e. first-generation) from all non-EU countries of origin, aged 15+ with at least 1 year's residence in seven EU countries, more specifically in 15 cities. 1 This analysis focuses on six countries and 13 cities: are Belgium (Antwerp, Brussels and Liege), France (Lyon and Paris), Hungary (Budapest), Italy (Milan and Naples), Portugal (Faro, Lisbon and Setubal) and Spain (Barcelona and Madrid). This analysis used the weighted sample of this representative survey, which was based on a country of birth sampling frame and comparable random sampling methods. 2 Further background on ICS is available in Annex A1.
One major advantage of ICS is that experiences of nationality acquisition are better captured in ICS than in most other transnational surveys. ICS asked about foreign residents' interest in acquisition of nationality and applicants' year, mode, and the experience and outcome of the procedure. One drawback of ICS is that the small number of countries limits the inclusion of independent variables about the national context (see Bryan and Jenkins 2013). As a result, the analysis could not include country-level contextual variables that would apply equally to all immigrants in the same country (e.g. electoral/government composition or public opinion).
The target group for this analysis is adults who were foreign citizens or became citizens as adults after immigration. This analysis excluded respondents who were children (ages 15-17) or applied for nationality as children (13% of applicants in the six ICS countries) because child applicants can apply through family-based modes, such as the extension of parental naturalisation. This analysis includes all foreign residents for two reasons: newcomers may be interested before they are eligible; second, eligibility itself is difficult-if not impossible-to assess with surveys. The analysis controls for eligibility with specific independent variables: residence duration, the residence requirement and the severity of the nationality law for each mode. All dependent and independent variables are summarised in Table A1 (see Annex).

Dependent variables
Based on the theoretical distinction between interest and ability, this analysis operationalises two distinct dependent variables, along with two robustness checks to further disentangle interest and ability. Table 1 summarises the variation across the six countries and 13 cities. Table 1 Description of sample on key nationality variables. The overall ICS descriptive results tended to identify greater variation between countries than between cities within the same country. For nationality acquisition, the apparent variation between cities has been addressed by Reichel  Ability to acquire nationality is measured as whether or not an immigrant has acquired the destination country nationality. Two ways of measuring ability are used in this analysis. The main models use a straightforward, broad definition of 'ability'. In our sample, 32% of immigrants has acquired the nationality, whereas 68% has not (Table 1). The shares of immigrants who acquired the destination country nationality as adults range from 7% in Italy to 45% in Belgium. This first measure includes naturalised immigrants, applicants, as well as interested and uninterested foreign residents. A robustness check will use a cleaner, narrower measure of ability where acquisition is measured only among immigrants interested in nationality (i.e. without those who have neither applied nor declared their interest to become citizens). According to such a measure, among interested immigrants, 40% has acquired nationality, while 60% has not. Together, these two measures clearly disentangle ability from interest.
Two ways of measuring interest are used in this analysis. The main models use a straightforward, narrow definition of 'interest' Interest to acquire nationality is measured by asking those immigrants who have not yet acquired or applied for nationality whether they want to become a citizen of their country of residence. On this narrow measure, 74% of immigrants in the sample has an interest in nationality acquisition, while 26% does not. The share of interested non-applicants ranges from 58% in Hungary and 59% in Italy to 86% in Portugal and Spain. A robustness check uses a broader measure of interest, on the assumption that immigrants naturalised as adults were de facto interested in nationality. This broader operationalisation of 'interest' combines all immigrants who acquired, applied or declared their interest to. In this case, uninterested immigrants foreign residents who neither applied nor declared an interest.

Independent variables
General demographic and socio-economic characteristics are captured by standard survey questions, such as age (years), gender (male/female), education (total years of education) and income (comparable/coping vs. difficult/very difficult). For example, socioeconomic status was measured based on education and current income. Immigrants' interest in voting ('Would you vote in the next election in the destination country?') was asked to immigrants both with voting rights (i.e. naturalised citizens and certain foreign residents in Belgium, Italy, Portugal and Spain) and without voting rights ('if you had the right to' was added to the question). The analysis includes the following migrant-specific characteristics: humanitarian migrants (self-reported first permit), duration of residence (years), proficiency in the official language(s) and knowledge of migrant-run NGOs (Yes/No). Language proficiency was assessed by the interviewer along a scale of whether the applicant spoke the official language (or any one of them in Belgium and Spain) not at all, a little, well or fluently.
Among the origin country variables, the relative socio-economic status of the origin country is measured using the Human Development Index [HDI]. Geographical distance was captured using the CEPII Geodesic Distance by the distance (by 1000 km) between the capitals of the origin and destination country. Origin country dual nationality provisions were coded with the MACIMIDE Global Dual Citizenship Database . All origin country variables are measured at the time of the survey.
For destination country nationality laws and procedures, 3 respondents were first individually coded to match their eligible mode of nationality acquisition using survey information. Four major modes can be distinguished from the survey: a) ordinary naturalisation; and facilitated naturalisation for b) refugees, c) spouses of citizens, and d) persons with cultural or historical ties or a very long residence duration (facilitated). Subsequently, each immigrant was coded for the applicable nationality law and procedure, based on indicators developed by the Global Citizenship Observatory. Nationality law was coded based on law [CITLAW] indicators that measure the relative ease or facilitation (score of 1) and difficulty (score of 0), based on residence, integration and economic requirements, among others (Jeffers et al. 2017). Nationality procedure was coded based on implementation [CITIMP] indicators on a similar scale that measures the opportunities and obstacles in the ordinary naturalisation procedure in terms of five dimensions: promotion, documentation, direction, bureaucracy and judicial review (Huddleston 2013). These two technical reports explain that the CITLAW scores involve expert weightings, while the scores for the CITIMP dimensions and overall score are based on simple averages. Both CITLAW and CITIMP were calculated based on publicly-available information and collected by the same national citizenship experts. The CITLAW and CITIMP scores for each indicator, as well as the national CITIMP reports, are available at the Global Citizenship Observatory.
All scores for destination country laws and procedures were measured at the time of the survey (see Table A3, Annex A4 and Table A5). Table 2 presents statistics for the eligibility by acquisition mode in all six ICS countries.
These CITLAW and CITIMP statistics and annexes show significant variation in laws and procedures across the six countries and across immigrants' eligible modes of acquisition. 4 Laws are generally inclusive for most immigrants in Belgium and Portugal as well as for spouses of nationals in Italy, refugees in Hungary and Italy and facilitated co-ethnics in Hungary, Portugal and Spain. Laws are most restrictive for ordinary applicants in Hungary and Italy and at different points in time in France. Procedures generally score lower than laws. The most inclusive procedures emerge in Belgium, Portugal and at different points in time in France, as well as for facilitated groups in Hungary and Spain. Procedures seem most restrictive in Hungary for other groups and in Italy across all groups.

Method of analysis
The analyses of the two dichotomous dependent variables use logistic regression 5 in a two-step model combining individual-level independent variables and country-level variables. In a first step (model 1a and 1b), the analysis includes destination country 3 The measurement of nationality policies focuses on the mode rather than the benefits of nationality acquisition because the variation in Europe lies primarily in the process rather than the benefits. In Europe, the benefits to foreign residents of nationality acquisition are often few from a legal perspective. Permanent residents have the same rights on paper as citizens in most areas except for full voting rights and full protection against expulsion.

Results
The first step of the analysis (Table 3) focuses on the individual-level determinants of the ability (model 1a) and interest (model 1b) to acquire nationality in order to assess the reliability of ICS' measurement of nationality acquisition to other previous studies. Immigrants' country-specific human capital is generally positively associated with ability to acquire nationality. As expected from other surveys, analysis of ICS shows that educated, long-settled and linguistically proficient immigrants are more likely to acquire nationality. Low-income groups are more interested, but not necessarily more likely to become citizens in practice. Similarly, low educated and recent foreign residents are more interested (model 1b), but less likely to acquire nationality (model 1a). Consequently, hypothesis 3b is only partially confirmed as human capital is positively associated with the ability but not interest. Human capital may play a more complex role in the nationality acquisition process than expected. Nationality's promise of security and equal treatment may be most convincing for the socio-economically vulnerable. But these vulnerable groups disproportionately face obstacles during the process, while those interested high-educated immigrants are more able to overcome these obstacles and succeed.
For the most part, socio-political capital is positively and significantly associated with ability. Interest in voting is positively associated with interest among foreign residents and ability among immigrants more broadly, while gender and the nationality of the spouse are positively associated with ability. Hypothesis 1b is only partially confirmed as political capital is positively associated with both interest and ability, while social capital is associated with ability.
As for origin country characteristics, in line with expectations (hypothesis 4), origin country dual nationality provisions are significant factors behind interest rather than ability. Similarly, immigrants from developing countries are more interested to acquire nationality. In contrast, those from neighbouring countries and refugees are likely to acquire nationality in practice.
The second step of the analysis (Table 4) drops the country dummies and adds the destination country nationality policy variables with ability (model 2a) and interest (model 2b). The inclusion of nationality policy indicators does not make a difference for most individual or origin country characteristics. For example, education still has a positive and significant relationship with ability and a negative association with interest. The one change is that residence duration is no longer a significant factor associated with interest among foreign residents, once the analysis accounts for the country's legal and procedural requirements. Comparison of models 2a and 2b (Table 4) confirms the hypotheses 1 and 2 about the different relationships between nationality policies and interest versus ability. Destination country nationality laws are a major factor behind nationality acquisition, while nationality procedures are a major factor behind the interest and, to some extent, ability. 6 These findings can be assessed in terms of the average marginal effects of destination country nationality laws and procedures in models 2a and 2b. Figure 1 displays the relevance of laws and procedures for ability by years of residence. The relationship between laws and procedures and acquisition is curvilinear, which is understandable as these laws and procedures are not expected to affect acquisition among recent arrivals or very long-settled groups (see Dziadula 2018). The difficulty of the legal and procedural requirements has the strongest relation to nationality acquisition among non-EU immigrants between 10 years' residence-the maximum de jure residence requirement within the six-country sample-and 30 years. For this group, an increase of 1 unit on the CITLAW nationality law scale generally leads to an increase of over 3 % in the likelihood of acquiring nationality (model 2a), while an increase of 1 unit on the CITIMP nationality procedures scale leads to an increase of over 2 %. Given that the CITLAW sample includes a 62-unit range of scores (from 0.38 to 1.00) and the CITIMP scale includes a 48-unit range of scores (from 0.17 to 0.65) nationality laws and procedures appear to be significant factors behind nationality acquisition. Figure 2 displays the relationship between destination country nationality procedures and origin country dual nationality policies, on the one hand, and interest in nationality among non-applicants, on the other. Here the association between the inclusiveness of procedures and outcomes barely increases over time. Nationality procedures emerge as a more important factor for interest than origin country dual nationality provisions. An increase of 1 unit on the CITIMP nationality law scale generally leads to an increase of over 3 % in the likelihood of foreign residents to be interested in acquiring nationality (model 2b).

Robustness checks
A number of additional analyses were run to confirm the robustness of these findings. 7 Given the small sample size and number of countries and groups surveyed, the first robustness check focuses on the relationship between nationality policies and interest/ ability when excluding specific countries or groups. The analysis was re-run dropping  Fig. 1 Average marginal effects of nationality laws on ability to acquire nationality. Calculations are based on Model 2a (Table 4) and include 95% confidence intervals one country at a time and then one group at a time (ordinary, spousal, refugee and facilitated). Table A6 presents the results of these 40 additional analyses and focuses on the coefficients for the two main policy variables in the main models, controlling for all other covariates. In 34 out of these 40 models, the coefficients for nationality law and procedures remain similar in significance. Not surprisingly, in terms of groups, dropping immigrants who fall under the 'ordinary procedure' most strongly affects the results on interest and ability. Most notable in terms of countries, dropping Italy meant procedures were no longer significant for ability or interest (pvalue = 0.070).
Next, the main models (models 1a and 1b, 2a and 2b) were re-run based on the different operationalisations of interest and ability by examining interest among foreign vs. all immigrants and then ability among interested vs. all immigrants. The analyses of ability were re-run with a more narrow sample excluding immigrants who self-declare as uninterested (models 3a and 4a). The analyses of interest were re-run with a broader sample including naturalised immigrants and applicants in addition to non-applicants (models 3b and 4b). Table A7 shows the results of these four additional analyses. With the narrow definition of ability among interested immigrants only, the relevance of all characteristics except refugee status remains stable (compare models 1a and 3a). After controlling for the institutional context (models 2a and 4a), the inclusiveness of nationality laws remains positively and strongly associated with ability, but the inclusiveness of procedures is no longer significantly associated with ability. When using a broader operationalisation of interest, the analysis is similar and confirms the positive association between procedures and interest and the absence of a relation between laws and interest (compare models 2b and 4b).
Finally, the analyses were re-run with different operationalisations of key independent variables. Robustness checks were run four times for nationality laws and procedures at the de jure residence requirement and at 10 years after arrival. Laws were further disaggregated to specifically capture the de jure residence requirement. Procedures were disaggregated in terms of access to the procedure (promotion and documentation) and difficulty of the procedure (i.e. bureaucracy, discretion, judicial review).
These different operationalisations of nationality policies confirm that the inclusiveness of nationality laws, including the residence duration requirement, is mostly associated with the ability (model 5a and model 6a) whereas the inclusiveness of nationality procedures is significantly associated with interest and ability (model 5b and 6b). These relationships hold even when laws and procedures are measured 10 years' after arrival. Disaggregating 'access' (Table A8, models 7a and 7b), ability and interest are linked to procedures both in terms of access and difficulty, although difficulty is less linked to interest than ability. The average marginal effects of these disaggregations are captured in Figures A1 and A2.
Looking further into the disaggregation of procedures (Table A8, models 8a and 7b), the strength of promotion measures is positively linked to foreign residents' interest in nationality, while facilitated documentation is positively linked to greater acquisition. The negative relationship observed between promotion and acquisition may be a case of reverse casualty; promotion may be most extensive and necessary where many foreign residents have not been able to apply but recently become eligible (i.e. post-2006 Portugal or post-2010 ethnic Hungarians).

Discussion and conclusions
This analysis provides significant theoretical, methodological and empirical contributions to the quantitative literature on nationality and integration policies. This article goes beyond the traditional 'cost-benefit' perspective on nationality acquisition to consider how the institutional context (re)shapes immigrants' interests and decision to acquire nationality. Theoretically, this article's theoretical and analytical framework helps to clarify the roles played by immigrants' motivations in the nationality acquisition or, more broadly, integration process. As noted by Bloemraad, nationality acquisition is determined by the interests and decisions of not only immigrants themselves, but also those of governmental and non-governmental actors to support nationality acquisition. This analysis' results suggest that administrative practice can act as a 'signaling' function that can reshape immigrants' underlying interests and social identity. Practices seem to play a stronger role than the laws on the book in shaping immigrants' perceptions of the benefits, costs, even the very meaning of national citizenship. The links between interest, ability and the main individual-level factors, most notably education, also deserve further investigation.
In terms of methodology, perhaps this analysis' main contribution is the disaggregation of the nationality acquisition process into interest vs. ability. Building on the few single-country studies dis-aggregating interest vs. ability, this article provided the firstever cross-country study of interest and ability among diverse immigrant groups and country contexts. This analysis tested different operationalisations of interest (e.g. including interested foreigners and naturalised immigrants) and ability (e.g. excluding immigrants uninterested in nationality), which can be tested and refined with other surveys in the future. Secondly, this article coded nationality policies as an individual rather than a purely national-level variable. This 'best fit' approach matching respondents to their eligible mode of acquisition by using respondents' year of arrival and individual-level characteristics. Lastly, this article is also innovative as one of the handful of cross-country analyses using the Immigrant Citizens Survey (ICS). ICS is one of the handful of migrant-specific cross-national surveys, with many migrant-specific variables related to nationality and integration policy (Reichel and Morales 2017).
Empirically, this unique international study on immigrants' interests and ability to acquire nationality finds that laws primarily regulate immigrants' ability to acquire nationality, while procedures primarily regulate their interest. Nationality proceduresespecially practices regulating access like documentation and promotion-emerged as some of the most significant factors driving interest among non-EU-born adult arrivals, regardless of their origin country's level of development and other key individual, origin and destination characteristics. Dual nationality restrictions were associated with interest rather than ability. In terms of ability, nationality laws are, not surprisingly, one of the most significant factors regulating nationality acquisition among interested adult arrivals from developing non-EU countries.
Reviewing the six European countries and four acquisition modes under scrutiny, this analysis has captured a new type of "implementation gap" in terms of the gap between immigrants' interest vs. ability to acquire nationality. Four distinct cases emerge: 'Promotion' case (e.g. for both long-settled immigrants in Belgium and Portugal and co-ethnics in Hungary, Portugal and Spain): Facilitated laws and facilitated procedures lead to highest levels of nationality acquisition and lowest gaps between interest and acquisition, as most immigrants are encouraged and thus able to become citizens. 'Exclusion' case (e.g. ordinary applicants in Hungary and Italy): Restrictive laws and restrictive procedures lead to the lowest levels of nationality acquisition and the lowest gaps between interest and ability, as many immigrants are no longer able or interested to become citizens 'Deterrence' case (e.g. spouses in Italy): The combination of facilitated laws and restrictive procedures lead to low levels and gaps, as many eligible immigrants are discouraged from applying but the few interested are able to meet the legal requirements. 'Deferral' or 'false promise' case (e.g. ordinary applicants in France): The combination of restrictive laws and facilitated procedures lead to low levels of nationality acquisition and the largest gaps between interest and ability, as procedures create interest among immigrants, but the legal requirements create insurmountable obstacles.
These four cases from six European countries revealed to what extent immigrants' interests and abilities can be reshaped simply by the nationality rules and procedures that apply to their specific mode of acquisition.
Finally, the results gives citizenship policymakers cause for reflection on the potential impacts of their laws and procedures. Policies not only create costs that affect immigrants' abilities to naturalise, as many policymakers and researchers would assume, but also create information and messages that inform immigrants' underlying interests. Countries are often inconsistent in their nationality laws and procedures. For example, nine European countries facilitate both their laws and procedures, while 13 facilitate the law, but not the procedure. Similarly, promotion and documentation policies are not related to the inclusiveness or restrictiveness of nationality laws (Huddleston 2013). Instead, most European countries have weak promotional measures for nationality and weak targeted integration support, despite the increasing integration obligations (Joppke 2007;Goodman 2010;Huddleston et al. 2015). For example, the CITIMP indicators suggest that few European countries provide enough hours of free language and civic courses for all types of immigrants to meet the requirements for ordinary naturalisation. Greater attention is warranted to nationality procedures and practices, particularly to changes in documentation, promotional measures and fees.