Curricular integration of academic and vocational education: a theory-based empirical typology of dual study programmes in Germany

In Germany, dual learning programmes are increasingly offered by higher education institutions. These programmes’ main characteristic and greatest challenge is their integration of academic and vocational learning. So far, this challenge has frequently been stated without specifying its exact nature and consequences for learners. The present study addresses this pedagogical research gap and examines the extent of variation in the degree of integration among dual study programmes. With reference to curriculum theory, the study develops an empirical typology of curricular integration in dual programmes. The data sample consists of 152 programmes at (dual) universities and universities of applied sciences. Data is analysed using hierarchical cluster analysis. Results indicate that the currently prevailing forms of curricular integration should best be differentiated according to five types. The five overlapping types of integration are located on a continuum ranging from parallelism through organisational linking to full curricular integration targeted immediately at students’ personal integration. The analysis confirms that there are problems with complying with integration standards set on the policy level. Above all, the study offers new insights on what marks the diverse integration landscape of dual study programmes. It proves that approaches to integration are more differentiated than previous research has shown.


Introduction
The main objective of dual study programmes in higher education (HE) is to offer students the benefits that result from integrating academic and vocational learning. While these dual academic programmes are formally part of tertiary education, the vocational elements are 1 3 typically located at the secondary level. According to the German Science Council (GSC, 2013), dual bachelor studies aim at systematically linking these two realms of learning. An increasing number of students in Germany favour dual studies (Authoring Group Educational Reporting, 2020), with universities of applied sciences (UAS)-the main provider of dual programmes-reporting stable growth rates. In 2005, the share of dual students at UAS was 1.4%; in 2017 it was 9.7% (Mordhorst & Nickel, 2019). According to the national student survey at universities and UAS, every second student can imagine studying dually (Multrus et al., 2017). Dual vocational programmes at the secondary level have a long tradition in Germany (Wolter, 2017). The recent expansion of "hybrid programmes" (Graf, 2017) at the intersection of the HE and the vocational system, in turn, is an innovation, since traditionally the two systems have been strictly separated (Baethge, 2006). The growth of dual programmes in tertiary education relates to a crisis of the dual vocational system and to the international trend of massification in postsecondary education: an increasing number of professions is moving out of the vocational and into the HE system.
Research on their structure suggests that the degree to which academic and vocational learning are integrated varies greatly between programmes (Krone, 2019;Langfeldt, 2018). Often the students themselves are challenged to connect their distinct learning experiences (Faßhauer & Anselmann, 2021;Kupfer et al., 2014). Different degrees of integration are generally possible if the programmes have coherent profiles. Parallelism of the two realms of learning, however, is not in line with the normative frame of these programmes. A lower degree of integration usually asks a higher transfer capacity of students and should be made transparent (GSC, 2013). Transfer capacity refers to a student's ability to make sense of and link vocational and academic learning experiences. As research on these programmes in general and on pedagogical aspects in particular remains scarce, the challenge of integration is frequently discussed without specifying degrees, types or consequences for learners. Until now, the few studies on the educational quality of dual programmes mostly reported students' perceptions (e.g. Krone, 2019;Nickel et al., 2018) and are often short of representative data (Langfeldt, 2018;Weiß, 2016). Commonly, research lacks pedagogical concepts of what integrating academic and vocational learning implies for the actual educational design of dual programmes (Faßhauer & Anselmann, 2021;Meyer, 2019).
In this paper, we investigate the differences in integration of academic and vocational learning. We focus on the pedagogical implications of different curricular characteristics, exploring the extent of variation in the degree of integration among dual study programmes. We contribute to the ongoing discourse on the design and the quality of dual programmes by first introducing a pedagogical perspective, where hitherto theory-based empirical contributions have focused on system-related aspects or structural issues (Graf, 2017(Graf, , 2018Krone et al., 2019;Schiller & Leišytė, 2020). Second, we contribute by identifying different types of curricular integration in dual programmes. To this end, we propose indicators grounded in curriculum theory (e.g. Kelly, 2009) and apply them in a cluster analysis. To understand typical curricular types of design, we examine dual bachelor programmes in the most common subject areas: engineering and economics (Hofmann et al., 2020). We draw on a representative data set from the German Centre for Higher Education (CHE) on dual undergraduate programmes. This makes the study the most complete empirical contribution in this field. As a result, we present a curricular typology of integration for dual bachelor programmes. With our paper, we show how curricular design elements support learners in integrating academic and vocational learning experiences. By adding a pedagogical perspective on the state of integration in dual programmes, it provides a differentiated picture of the status quo in Germany and an analytical framework for international policy makers, researchers and dual programme designers.

Literature review
In the German education system, dual educational programmes have a long tradition in initial vocational training at the secondary level (Wolter, 2017). Situated in "the dual system of vocational education and training (VET)" (Baethge & Wolter, 2015, p. 97), these vocational programmes combine "training on-the-job" and "school-based learning in vocational colleges" (Sloane, 2014, p. 402). For many years, VET has been the backbone of the German educational system with entrants well above those to HE. This distribution changed over the last decades and in recent years entrants to HE have been higher than entrants to VET (Authoring Group Educational Reporting, 2020). Tertiary dual programmes must be perceived in the context of HE massification and the simultaneous "apprenticeship crisis" (Deißinger, 2006, p. 181) in VET. One of the reasons for the crisis is companies' declining interest in the VET system (Deißinger, 2006). While learners and companies increasingly ask for academic degrees, many still acknowledge the benefits of VET (such as immediate access to a job or trainees' workforce), making dual programmes at the tertiary level a relevant phenomenon.
To grasp the variation in the degree of curricular integration among dual programmes, we have to consider the dual character of these programmes not only structurally but also in pedagogical terms. For several years now, scholars have noted that the discourse on how to design dual academic programmes lacks a focus on pedagogy (Faßhauer & Anselmann, 2021;Meyer, 2019;Mordhorst & Gössling, 2020), i.e. the relationship between structural decisions and the individual learner's development. Until now, there has been no comprehensive theoretical framework in HE which focuses specifically on duality, i.e. the question of how to design the integration of academic and vocational learning. Such a framework, however, is necessary to delineate what duality or integration mean and which characteristics of these concepts are present in the curricular designs as well as the pedagogical practices of dual programmes. To develop theoretical categories which allow for a pedagogical understanding of duality and integration, first, we expound on the German dual VET system. Second, we refer to curriculum theory, deducing general curricular dimensions relevant for shaping educational experiences in dual programmes. Third, these dimensions are further qualified with reference to policy recommendations. Fourth, we refer to the state of research on curricular integration in dual programmes.

Duality in vocational and higher education
The German dual system of VET is highly regulated and complex. The 16 federal states are each responsible for designing syllabi for vocational schools, while training regulations for companies are the responsibility of the federal government (Sloane, 2014). Conceptually, the term dual system suggests that two systems collaborate to form a whole, which has been emphasised since the 1960s (Euler et al., 1999). Duality goes beyond governance or the organisational combination of two venues of learning and extends to the teaching and learning activities (Sloane, 2014). While the legal framework for VET emphasises this extensive duality, the degree to which it is implemented varies (Euler et al., 1999). Zabeck (1996) distinguishes between dualism and duality. Where the former suggests parallel activities of schools and companies with hardly any cooperation, the latter implies intense collaboration.
The VET-related discourse on duality provides basic categories for understanding degrees of integration between academic and vocational learning. At the same time, the transferability to dual study programmes has its limits (Faßhauer & Anselmann, 2021). This is largely due to the different regulatory settings of HE and VET and their consequences. The German HE system is binary, comprising universities and UAS. The system is further characterised by academic freedom of teaching and research as well as relatively autonomous higher education institutions (HEIs). While the federal states exercise oversight and accreditation provides some quality control of study programmes (Kehm, 2018), there is no direct regulation regarding educational content and pedagogies.
From a regulatory perspective, there are two types of dual academic programmes, which differ in regard to the contracts students sign with corporate partners and the awarded degrees. In both programmes, students gain a bachelor's degree and enrol in a HEI. In so-called training-integrating programmes students sign a contract with a company for a legally regulated profession and obtain an additional VET degree. In practice-integrating programmes students only enrol for the university degree. Besides their status as HE students, they have a contract for extended work placements with a corporate partner (GSC, 2013).
The German Standing Conference of the Ministers of Education and Cultural Affairs (GCMEC, 2017) defined the criteria for the accreditation of dual programmes in an exemplary statutory order. This statutory order (GCMEC, 2017) defines the following aspects as crucial dimensions for carrying the label dual: Besides the academic principle, the core element characterising dual studies is the combination of at least two venues of learning. It further indicates that duality in the sense of organisational linkages between the academic and the vocational venue of learning provides the basis for an integration that should extend to learning content. As opposed to VET on the secondary level the organisational and the curricular side of integration are defined as two connected, but separate elements which are not standardised.
Thus, in the context of dual academic programmes, the term duality refers to organisational linkages between HE and VET, remaining rather unspecific about content and pedagogies. It requires adequate concepts to investigate how learners are supported in linking and integrating the learning experiences in dual programmes. Curriculum theory can provide these concepts. The need for such an approach is underpinned by the fact that most dual programmes encompass some degree of organisational linking, while problems occur with the systematic integration of learning content (German Accreditation Council (GAC), 2020). The principles of academic freedom and autonomy of HEIs make a greater variety of approaches to integration more likely. Additionally, dual study programmes were never strongly supported by political initiatives (Nickel et al., 2018). It is up to each HEI to spell out how to accomplish duality and integration. To sum up, HEIs are granted much more autonomy in how to run their dual programmes than the VET institutions (Graf, 2017).

Curricular integration in higher education
Curriculum theory is concerned with how to develop broad educational objectives into a programme which provides experiences that help learners to achieve those objectives as best as possible (Kelly, 2009). Generally, the curriculum provides a structural framework (i.e. modules, workload, assessment modalities) as well as an institutional framework (i.e. expectations towards learners and educators) in which educational activities take place.
The literature defines common elements of curriculum to include goals, content, sequence, integration, and assessment. Goals define the outcomes expected from an educational programme (Diamond, 2008). Content refers to the subject matter selected to foster the goals (Lattuca & Stark, 2009). Sequence deals with the vertical relationships in the curriculum and the systematic organisation of content over time (Goodland & Su, 1992), for instance, over the entire length of a bachelor's programme. Integration intends to evolve a curriculum in a way that its elements mutually contribute to a holistic learning experience (Goodland & Su, 1992). In the case of dual programmes, integration refers essentially to the integration of academic and vocational learning experiences. While the "ultimate integration is in the learner […] the process is aided presumably by the way in which the curriculum components are organized" (Goodland & Su, 1992, p. 330). Thus, we can differentiate between personal integration and curricular integration. Assessment refers "to judgements about student learning" (Harlen, 2016, p. 693).
These categories provide a frame of reference for analysing programmes. A pedagogical analysis of dual programmes would investigate how both the academic and the vocational dimensions become visible in the curricular design. Integration is a core category for investigating dual programmes as it refers to all the dimensions mentioned above and qualifies them in regard to the relationship of academic and vocational components. Here, the core question is (how) do curricular design elements support learners in integrating the academic and the vocational learning experiences?

Characteristics of curricular integration in dual study programmes
While curriculum theory provides overall categories for a curricular analysis of dual programmes, these dimensions need to be further qualified concerning the pedagogical implications of the dual character. The GSC (2013) suggests measures to systematise dual studies ranging from governance aspects via organisational measures to curricular elements. In Table 1, we show those measures relevant for designating curricular integration and duality (organisational linking). We group the measures by the dimensions from curriculum theory. In addition, we differentiate between organisational and curricular integration-inherent in curriculum theory as well as in the policy discourse (Kelly, 2009;GSC, 2013).
Regarding organisational linking, the measures mentioned below are emphasised (GSC, 2013): • Stable contractual relations with corporate partners: cooperation is regulated through contracts with the corporate partners who train the students • Exchange in cooperation committees with actors from HEI and vocational institutions: regular meetings in committees can foster organisational and learning-related cooperation • Cooperation in admission processes: cooperation committees can support a joint admission which is otherwise often exclusively carried out by the corporate partner for the training part; in return, HEIs need to discuss their admission criteria with the corporate partners; the final decision on the admission must remain with the HEIs With respect to curricular integration, the GSC (2013) provides the following measures: • Coordination of curricula and learning goals: this measure also encompasses decisions on sequencing and the integration of training by the corporate partner in the study plan • Comprehensive learning concepts, which encompass a regular exchange between actors in the academic and vocational field: such concepts entail, for instance, joint study projects offered by HEI and corporate partners • Special classes for dual students, if conventional and dual students study together in a programme: dual students must be supported through tailored modules in integrating the learning experience at the corporate partner • Recognition of phases at corporate partners as study experience, formalised through credit points: recognition must be anchored in the study plan The introduced characteristics of curricular integration inform the analysis of dual programmes, as they qualify the meaning of the terms duality and integration.

Empirical evidence on curricular integration in dual study programmes
In this section, we review empirical research on dual programmes in Germany using Table 1 as a frame of reference to provide an overview of the state of research on characteristics relevant for our analysis. Theoretical concepts on dual studies are not reviewed as there are hardly any (Gerstung & Deuer, 2021;Mordhorst & Gössling, 2020;Schiller & Leišytė, 2020) and none refer to curriculum theory.
As far as we know, there is no empirical study investigating curricular integration as a core theme. Extant research often focuses on structural issues within systems and on an institutional level (Graf, 2017(Graf, , 2018Krone et al., 2019;Schiller & Leišytė, 2020). While the measures in Table 1 are occasionally part of such studies, they have not been investigated from the viewpoint of curriculum theory.
Organisational issues with the linking of different institutions are frequently addressed (Kupfer et al., 2014;Langfeldt, 2018). A small-scale study on dual students (n = 14) found that around two thirds report a tight cooperation between workplace and HEI (Nickel et al., 2018). In a study on dual engineering and economics programmes, 30% of the companies interviewed (n = 292) reported to be part of at least one committee for cooperation. Using document analysis, the same study revealed that all dual programmes have some sort of cooperation committee (Langfeldt, 2018). Qualitative empirical evidence from case studies at UAS describes cooperation to be loose in many dual programmes. HEIs and corporate partners report cooperation structures to have a low degree of formalisation based on contracts, committees, etc. (Kupfer et al., 2014). Comparing the results of these two studies reveals that the question whether formal instruments such as committees are in common use has not been fully resolved yet. However, the publication dates of the studies suggest that there might have been some shift in recent years towards a wider use of committees.
An investigation on the potential of dual science, technology, engineering and mathematics programmes reported in a qualitative part that the level of combination of academic and vocational learning ranges from no coordination between HEI and corporate partner, via non-committal recommendations by the HEI to reflection modules for phases at the partner company. This description hierarchically arranges organisational linking and curricular integration, reducing integration to the structural aspect of modules. Staff from HEIs in this study pointed out that integration is especially hard to establish in those programmes which combine regular and dual studies (Wolter et al., 2014).
1 3 Kupfer et al. (2014), Langfeldt (2018) and Krone et al. (2019) found qualitative and quantitative evidence that dual programmes often lack curricular integration. Only a quarter of the students who participated in the online survey (n = 4125) by Langfeldt (2018) judged the combination of learning content in their study programme to be 'good' or 'very good'. Likewise, Krone et al. (2019) report students (n = 9285) to be only partially content with the integration of academic and vocational learning in their dual programmes. 79% of the companies asked (n = 280) in an online survey by Kupfer et al. (2014) reported HEIs to be solely in charge of academic learning. 91% agreed that corporate partners have no support from HEIs when it comes to the vocational education. Thus, the empirical studies seem to confirm that curricular integration is a particularly difficult challenge (cf. GAC 2020).
To sum up, extant research lacks representative empirical data on dual programmes (Langfeldt, 2018;Weiß, 2016). Krone et al. (2019) seem to be an exception but do not address the topic of curricular integration as a core theme. Until now, there has been no systematic survey investigating the characteristics mentioned in Table 1. Thus, a quantitative survey exploring the issue of curricular integration in dual programmes based on pedagogical criteria is a gap in the research landscape with important consequences, which has yet to be filled. Currently, challenges with integration are lamented, but their specific nature and consequences for learners are not specified. This paper analyses the differences in integration from an educational perspective. We investigate the following research question: How (and to what extent) does the degree and nature of integration among dual study programmes differ? Thus, we focus on curricular integration and organisational linking, as they are a prerequisites for personal integration. We propose indicators grounded in curriculum theory and apply them in a cluster analysis. As a result, we intend to develop a typology of curricular integration for dual bachelor programmes. Advancing the analysis of these programmes is relevant because more and more students enrol in these programmes (Mordhorst & Nickel, 2019). Their integrative approach is an innovation, since traditionally the two systems of HE and VET have been strictly separated (Baethge, 2006).

Sample and procedure
The research was conducted as a cross-sectional study on the integration of vocational and academic learning in dual programmes at German (dual) universities and UAS. The sample covers programmes in engineering and economics as these are the most common subjects of dual studies (Hofmann et al., 2020). The data was provided by the CHE. All university departments of dual programmes in engineering and economics registered in the database for study programmes by the German Rectors' Conference (GRC) were asked to participate. Programmes in this database are "state-approved and/or accredited" (GRC, 2020). Accredited programmes not listed there were added manually to obtain a complete sample. The data was collected from May 2018 to January 2020 by the CHE. The response rate was 72.3%, equalling 219 questionnaires. Such a response rate is high for online surveys among university staff (Kaplowitz et al., 2012). In total, 66 cases missed data in single variables. We had to exclude these cases from the sample due to data requirements in SPSS for the method chosen in the final data analysis. One case was excluded during data preparation. Hence, a total of 152 cases were included in the final sample (see Table 2). The distribution by type of governing body and HEI reflects the general characteristics of the dual programmes in engineering and economics; also, the ratio of engineering and economics fits the real distribution (GRC, 2020). There is no specific data on the relative proportion of practice-versus trainingintegrating programmes in engineering and economics. However, data on this distribution is available for all subject areas together, which shows that regarding this criterion our data set is representative (Hofmann et al., 2020). Overall, we regard the sample as representative of dual programmes. The data was checked twice for plausibility. After the first plausibility check, the university departments were asked by the CHE to review their data and add missing variables. We carried out the second plausibility check after the survey was conducted, before proceeding to analyse the data. Additionally, we verified some variables manually comparing open-ended text items with the closed questions used for analysis.

Measures
In total, eleven variables were included in the analysis (see Table 3), all of which are binary. While some items were binary in the questionnaires already, others had to be downscaled to allow for the intended cluster analysis. The nominal characteristics were transformed to binary items using a binary split. We applied a median split to transform the continuous variable 'number of students in study programme' as the box plot for the variable showed many outliers. Thereby, we optimised discrimination without losing too much information or having to expect distortion when analysing our data, as the nominal items were ideal for a binary split.
The variables operationalise the characteristics of organisational linking and curricular integration. Most of the variables cover curricular dimensions due to the paper's focus on curricular integration. All items were derived from the literature on dual programmes. Two organisational variables on duality are also included (sample item: 'Is there a written agreement on the institutional exchange between HEI and the corporate partner?'). Nine items refer to curricular integration (sample item: 'Does the study plan identify study content to be provided by the corporate partner?').

Analyses
We chose hierarchical cluster analysis (HCA) to group our cases as it fits binary, mediumsize data sets and groups cases in a stage process without a fixed number of clusters. Cluster analysis is commonly used for typology studies in higher education (e.g. Bahr, 2010;Inkelas et al., 2008) and allows for a sample-driven approach. Providing the degree of distance among cases, cluster analysis groups similar cases into the same clusters. We decided against using two-step cluster analysis or k-means, as the algorithm for the two-step method is hardly documented and k-means asks to define the number of clusters beforehand. The survey data were analysed using SPSS Statistics 27. We considered other methods for typology studies used in HE research such as latent class analysis (LCA; e.g. Custer & Akaeze, 2019; Denson & Ing, 2014) and factor mixture modelling (FMM; e.g. Hatch & Bohlig, 2016). While LCA is applicable with categorial data, it ignores heterogenous facets of data and is not sample-but model-dependent (Denson & Ing, 2014) and therefore not fit for our purpose. Similarly, FMM is a model-based approach (Hatch & Bohlig, 2016), and thus no option for our analysis either.
As cluster analysis is an exploratory approach, we tested different cluster solutions before finding a robust grouping. For different options, we changed the proximity measure and the merging algorithm. To test for outliers, we carried out an HCA twice, once using the Simple Matching Coefficient and then the Euclidian Distance as the proximity measures, applying both times the agglomerative merging algorithm Single Linkage. Two different proximity measures were used to yield robust results. Single Linkage was used as the merging algorithm, because it can identify outliers. We excluded one case from the sample based on the results. Before doing so, however, we carried out a manual plausibility check as well as a cluster analysis with the outlier (Rapkin & Luke, 1993), resulting in a clear decision to exclude it. For identifying clusters with mutually related variables in the final HCA we applied the agglomerative merging algorithm Complete Linkage. The Simple Matching Coefficient was chosen as the proximity measure, as it allows to simultaneously consider all unanimous variables whether an item applies or not. In a first step, the number of clusters was not determined beforehand, as we had no criteria for estimating how many clusters would make sense. We checked for plausibility and considered not only the dendrogram, but also the scree plot (see Appendix Fig. 2) to deduce a statistically meaningful number of clusters, identifying five clusters as the best number of clusters. In a second step, we processed the data once again with the same algorithm and proximity measure and the fixed number of five clusters resulting in a robust cluster solution with a high homogeneity within the clusters and high heterogeneity between the clusters. We compared the variables used for clustering between the resulting clusters to investigate the cluster properties. This investigation is like a validity check of the cluster solution. We used crosstabs as descriptive presentation, Chi-Square tests for checking significant difference and Cramer's V as an effect size measure. We found out that all variables used for the clustering show statistically significant differences between the clusters (cf. Appendix Table 5). Additionally, we did further comparisons between the groups concerning relevant variables not included in the cluster analysis. Again, we used the procedure described above. With this analysis, we characterised the groups further and checked for possible differences between the clusters. This helped us to better understand the different groups and their defining characteristics.

Results
In this section, we present the five-cluster solution. Each of the 152 programmes was assigned to one of five discrete clusters. Table 4 gives an overview of the clusters. It indicates the percentage of programmes which are fully dual (no regular students enrolled). The main integration characteristics refer to the attributes identified in the cluster analysis. A cluster's degree of integration draws on its overall scoring in the analysis, referring to both categories of organisational linking and curricular integration.
Cluster A 'Incoherent curricular integration in programmes mixed with non-dual programmes': Regarding organisational linking, this cluster is characterised by a relatively low share of contractual relations on institutional exchange between HEI and the corporate partner (60.0%). However, it has the highest share of collaborative admission of HEI and corporate partner (26.7%) of all clusters. In terms of curricular integration, e.g. regarding collaboration for integration, the cluster lacks transparency. For instance, the study plan does not provide content to be studied at the corporate partners. Yet, in more than half of the programmes, staff from the partners regularly teach in HEI and in 46.7% of the programmes students earn credit points for learning activities at the partner company. The cluster comprises only programmes where dual and regular students study together. In 93.3% of the programmes, dual students study partly in separate classes without regular students to foster curricular integration of vocational and academic content. Programmes in this cluster are mostly smaller with no more than 58 students (80.0%). Regarding the regulatory classification, most of the programmes (40.0%) can be studied both as practiceand training-integrating programmes. These programmes are called mixed programmes in the following. A typical programme in this cluster would be a management programme at a private UAS with some curricular integration elements, such as recognition of training at the corporate partner formalised through credit points. However, the cluster is incoherent because often the study plan does not indicate the recognised content.

Cluster B 'Assessment-based curricular integration in programmes mixed with non-dual programmes':
The cluster is characterised by a low degree of organisational linking, e.g. 19.0% of the programmes have contracts with the corporate partners on institutional exchange regarding their cooperation. Most variables also illustrate a lack of curricular integration. For instance, 9.5% of the programmes rely on agreements related to goals and sequence determining how to coordinate study content, classes and assessments. In the Well-regulated organisational linking and curricular integration High D (n = 28) 7.1% Good organisational linking, but especially strong curricular integration High E (n = 21) 14.3% Organisational linking, hardly any curricular integration Low dimension content, only 9.5% of the programmes rely on special classes for dual students. This is unexpected, as in all programmes in this cluster dual and regular students study together and the number of dual students per programme is rather high. In 57.1% of the programmes, between 59 and 1270 students are enrolled. 90.5% of the dual programmes regulate the assessments of study content provided by the corporate partners and 85.7% coordinate assessments with them. Thus, integration in this cluster is essentially assessment-based. With respect to regulatory classification, programmes in this cluster primarily lead to a VET (71.4%) next to the academic degree. An example for a typical programme in this cluster would be a public UAS programme in mechanical engineering integrating a regulated VET degree in industrial mechanics mainly through assessment practice.
Cluster C 'Clearly regulated, coherent curricular integration in fully dual programmes': Regarding organisational linking, dual programmes in this cluster are characterised by stable contractual relations (all programmes). The degree of curricular integration is also high: Related to goals and sequence, in 92.5% of programmes, agreements regulate how to coordinate study content, classes and assessments. Regarding collaboration for integration, content in the study plan is explicitly assigned to the corporate partners in 67.2% of the cases and 71.6% of the programmes have accredited modules at the partners. In no other cluster company staff teaches more often at the HEI (89.6%). Regarding content, most of the programmes are fully dual (77.6%). This cluster consists primarily of larger programmes with at least 59 students (70.1%). All programmes determine how to assess content provided by the corporate partners and coordinate assessments with them. In 74.6% of the programmes, students earn credit points for learning activities at the partner corporation.
Considering the regulatory classification, most of the programmes are practice-integrating (70.1%). Typical for this cluster would be a large, fully dual and coherent practice-integrating programme in business management at a public dual university or public UAS with a high degree of regulation on the organisational and curricular level.
Cluster D 'Holistic, transparent curricular integration in programmes mixed with non-dual programmes': Programmes in this cluster have a relatively high degree of organisational linking, e.g. HEI and corporate partners collaborate in 78.6% of cases based on a written agreement. Variables reveal holistic curricular integration patterns. For instance, regarding collaboration for integration, in 85.7% of cases content is directly assigned to the corporate partners in the study plan and 78.6% report to have accredited modules at the partners', both the highest scores in comparison. Regarding the content category, in 7.1% of the cases, students study in fully dual programmes. In 50.0% of programmes, students learn in separate classes without regular students. Regarding student numbers, the cluster is in the middle range: in 78.5% of programmes, there are 13 to 139 students. Coordination of assessments (96.4%) is common. It is the only cluster with a higher rate of coordination of assessments than guidelines (85.7%). Regarding regulatory classification, 39.3% of the programmes are mixed and another 35.7% lead to a vocational degree in addition to the academic degree. Typical for this cluster would be a public engineering programme designed as a dual training-(and practice-) integrating and as a regular programme with a transparent and holistic curricular integration. It could be provided by a UAS or a university.

Cluster E 'Mainly organisational linking in programmes mixed with non-dual programmes':
Regarding organisational linking, institutional cooperation is aided by written agreements in 66.7% of dual programmes and 19.0% of the programmes practice admission collaboratively-both intermediate scores. Results depict a low degree of curricular integration in this cluster. For instance, looking at the content, 14.3% of the programmes in this cluster are fully dual and 9.5% have separate classes, which is low considering the share of programmes combined with regular programmes. The cluster properties provide 76.2% smaller programmes (0 to 58 students). 23.8% have guidelines on assessing study content provided by the corporate partners, but none coordinate assessments with them (the overall lowest scores). With respect to the regulatory classification, 47.6% of programmes in this cluster lead to a vocational in addition to the academic degree. Typical for this cluster would be a public or private UAS or university programme in engineering offered as a regular and as a dual study path, lacking support for students with integration.
To sum up, the analysis yielded two clusters with a high degree of curricular integration: clusters C and D. Programmes in cluster A show some elements of organisational linking and curricular integration but lack transparency. Clusters B and E have a low degree of curricular integration.

Discussion
Curricular integration of academic and vocational learning is both a core characteristic and a great challenge for designing dual programmes (Mordhorst & Gössling, 2020;Nickel & Püttmann, 2015). This study demonstrates how curricular design elements support learners in integrating academic and vocational learning experiences.
Overall, the typology developed in this study confirms that the degree of integration varies significantly between study programmes labelled as dual (cf. Krone, 2019;Langfeldt, 2018). Our analysis found different forms of curricular integration. As discussed, the concepts from VET are only partly applicable to dual academic programmes. The different institutional set-ups of dual academic programmes and VET have direct effects on the curriculum level. Duality in VET goes beyond the organisational combination of two venues of learning and extends to the learning activities through an extensive legal framework. Due to the principles of academic freedom and institutional autonomy of HEIs, legal regulations on duality in dual study programmes remain rather unspecific about content and pedagogies, asking for a differentiated perspective on organisational linking (duality) and curricular integration.
Therefore, the divergent types of curricular integration we identified could be placed on a continuum ranging from parallelism through duality to full curricular integration targeting students' personal integration directly (see Fig. 1).
Duality as the core category for organisational linking refers to the cooperation of HEI and corporate partners realised through measures such as committees. These measures are important to support strong structural links between the actors and usually have no direct impact on students. Yet, some of these measures affect students directly, such as admission parallelism d uality curricular integration cluster E cluster C cluster D cluster B cluster A Fig. 1 Continuum of curricular integration procedures. Our analysis reveals that all programmes rely on some sort of organisational linking for the cooperation of HEI and corporate partners (cf. GAC 2020; see Fig. 1). Additionally, our results confirm the problem that there are programmes which hardly go beyond duality (cf. GAC, 2020; see cluster E), lacking curricular integration elements. A lack of curricular integration conflicts with the core promise of dual learning (GAC, 2020). In turn, programmes with a high degree of curricular integration also have stable contractual relations with cooperation partners (clusters C and D). This supports the assumption that organisational duality is the basis for curricular integration (cf. GSC, 2013). However, organisational duality does not guarantee curricular integration.
Regarding curricular integration aiming at personal integration, results indicate that establishing a systematic integration is more challenging in programmes combining regular and dual studies (cf. Wolter et al., 2014). Programmes mixing both-different types of dual programmes as well as dual and regular programmes-are especially difficult to design. While such a differentiation asks for a curricular response with measures such as specifically tailored modules for dual students, this is not common in all the clusters. Some programmes rather seem to follow a very economical approach, relying on similar study plans for regular and dual as well as for practice-and training-integrating programmes. A small number of modules are offered in different programmes, resulting in quality constraints and blurry programme profiles. For instance, purely assessment-based integration (cluster B) is not a form of systematic curricular integration (similar degree of integration as cluster E). Integrated assessment does not support students in the process of integrating their learning experiences. It expresses, however, an expectation for such intellectual integration. Additionally, measures such as separate classes for dual students, credit points for learning content provided by corporate partners or having corporate staff teach at the HEI is not necessarily a sign of quality, if students do not know which content is provided by the partner. Especially practice-integrating programmes without clearly regulated work placements are more likely to align their goals and content with company-specific rather than professionspecific skill demands (Graf, 2018). Hence, transparency of learning content and concepts is especially important in these programmes. However, there are programmes with an active role of corporate partners and no such transparency (see cluster A). In contrast, the high share of programme-specific agreements in cluster C with 70.1% practice-integrating programmes might be a positive sign, indicating that HEIs take on their responsibility in those programmes where the work-based part is not based on regulations in VET.
The results also illustrate that training-integrating programmes have a lower degree of curricular integration than practice-integrating programmes (cf. Langfeldt, 2018). However, there is no clear tendency for an overall low degree of integration, as all formal types of dual programmes can be found in all the clusters. Yet, the nature of integration varies according to the regulatory classification (see clusters C and D). Whether the regulatory classification grants much autonomy in designing the work-based part of the programme (practice-integrating programmes) or whether there are legal regulations standardising the vocational part of the programme (training-integrating programmes) affects the integration design.
A systematic integration-as conceptually defined for dual programmes-may be achieved through curricular measures on different levels, e.g. by designing programmes which are exclusively for dual students (cluster C) or by establishing programme structures in mixed setups that support the learning experience through additional elements specifically designed for dual students (cluster D). We assume that coherent curricular integration fosters personal integration. However, it does not guarantee an integrated learning experience. How students perceive learning in those programmes, which are formally characterised by a holistic curricular integration, is another research gap, yet to be addressed.

Limitations and future research
In the following section, we discuss the limitations of the study, its implications for future research and the generalisability of the findings. The study is limited in three ways. First, as the study is based on secondary data, after deducing criteria for analysis, we assigned fitting variables from our data set to the categories. Most of the items cover the criteria derived from the literature very well. However, as extant databases on dual programmes are not pedagogical, so are some of the items. This was problematic in one case: While our category from curriculum theory was goals and sequencing, as there was no better fit, the item we selected refers to content, classes and assessments, leaving goals and sequencing aside. Educational goals of a programme, however, are essential, as they often serve as a starting point to design sequencing and content. Therefore, our criteria derived from the literature review could inform future quantitative studies on curricular integration of dual programmes.
Second, the quantitative data says little on the concrete realisation of curricular integration including cultural aspects of teaching and learning (cf. James, 2014). Aiming at advancing integration, it could be interesting to address questions such as: What do comprehensive learning concepts look like? Which role do goals and sequencing play? How do institutional and programme cultures enable the cooperation between HEIs and partners? These questions can lead to the overall research question: What are design principles fostering curricular integration in dual programmes? To resolve the question, case studies are necessary.
Third, our study is limited regarding subjects and groups of persons questioned. While economics and engineering programmes make up most dual programmes and are thus representative, future research could show whether the typology fits for other subjects too. Computer science and health care programmes would be interesting to investigate, as they are other relevant subject groups in dual studies (Hofmann et al., 2020). While the study focusses reasonably on HEIs, it would be interesting to look at learners' experiences regarding the insights from our analysis.
Despite these limitations, the study contributes to our understanding of curricular integration in dual programmes. Altogether, the study is valuable, because it yields a robust and differentiated typology on the integration of academic and vocational learning. It is the first pedagogical empirical study on German dual programmes in HE. By adding a differentiated view on the state of integration in dual programmes it provides new information for policy makers, researchers and dual programme designers alike. The insights are necessary for the ongoing process of institutionalisation (Graf, 2018) of dual programmes becoming a special type of many educational programmes in a differentiated HE system. The analytical framework can inform quality monitoring and policy making. Results are also relevant for students' orientation. On an international level, the findings are fruitful for any dual programme regardless of the HE system, e.g. a professional degree programme on the masters' level integrating job experience. Yet, those findings targeting organisational aspects depend on governance constellations and are therefore not easy to transfer. 1 3 Additional variable based on information from module handbooks manually collected in 2020. The data in this variable is limited to some degree because 20 of the considered module handbooks were published later than March 2020 and therefore after the main survey was conducted. Can students earn credit points for learning activities at the corporate partner other than a semester or a bachelor's thesis in cooperation with the corporate partner?
Credit points Not included in HCA due to separate data collection