## 3 Research Approach  
To answer the two research questions derived in Section 1, the Design Research Methodology (DRM) proposed by [PERSON] and [PERSON] [47] was used. DRM was selected due to the iterative, flexible research approach and context specific guidance. To adequately incorporate industrial practice it is enriched by implications from [PERSON] [48]. He focuses on applied research and encourages continuous incorporation of practitioners and an extensive analysis of the application context. For each research question, DRM was utilized separately, but not independently. The overall research approach and the related steps of DRM are illustrated in Figure 5.  
Results of the initial step \"Research Clarification\" were generated by structured literature research following the approach of [PERSON] and [PERSON] [49]. Details on search terms can be found in Figure 5.  
Figure 4: Conceptual model of requirement change risk factors. Within the second step \"Descriptive Study I\", initial reasoning of the research field is extended by further theoretical and practical investigations [47]. For the theoretical perspective, a literature analysis was conducted for both RQs. In addition, interviews with industrial partners from various companies were conducted to get insights into what causes application effort, current state of tools and methods used and needs from industrial application. Companies included SMEs as well as larger companies from various industrial branches such as additive contract manufacturing, machinery and equipment engineering, automotive development and forming technology. Based on this in-depth analysis, a method for systematic assessment of requirement change risk and a software prototype to support the application of the method were developed within the \"Prescriptive Study\". The assessment included a priority score and a dependency score. The priority score combined change impact and exogenous change likelihood. It was calculated according to a Failure Mode and Effect Analysis (FMEA) logic, which is well known in industrial practice and enables to quantitatively merge different influence factors of change risk [43; 50]. The dependency score was used to assess change propagation and endogenous change likelihood. The two-stage approach relies on a requirement structure matrix [51]. Within the first stage, the active and passive sum of each requirement was assessed [25; 52] and used for initial categorization. For further differentiation between requirements of one category, the Euclidean distance was used [53]. In a multiple case study approach according to [PERSON] [54], three industrial product development projects were accompanied and used as a data source. Case studies were provided by four industrial partners from the third-party funded research project \"OptiAMix\". Within this project, a novel approach towards holistic product development, topology optimization and a digital process chain for additive manufacturing was developed. Part of this was a generic requirement change risk assessment which  
Figure 5: Research approach based on [47]. was tailored for, but not limited to, additively manufactured products. The three case studies cover a large range of both, enterprise characteristics and industrial branches to ensure broad applicability in industrial practice. Details on the three case studies are shown in Table 1 below. A multiple case study approach was chosen to ensure broad applicability in industrial practice by considering requirements from practice for both, method and software and from a range of industrial branches and enterprise characteristics. Besides the requirements from those case studies, they were used to test interim results in an industrial setting and generate data for the evaluation within \"Descriptive Study II\". Within the final step \"Descriptive Study II\", data acquired during the case studies was analyzed with regard to the potential improvement by applying method and software in industrial practice.