# On the Road to Circular Public Procurement: Case, Variations, and Potential Actions in Germany
## 2 Materials and Methods
### Research Method  
In order to answer the research questions on sustainable circular tyre procurement, the problem-centered interview, according to [43], was chosen. An interview guide was prepared to discuss procurement processes, barriers of circular tyre procurement, and the need for support to stimulate a more circular public procurement. Box 1 provides an overview of the interview topics. The research was conducted within the publicly funded German research project ConCirMy (Configurator for the Circular Economy), which aims to promote the tyre CE by the development of tyre configuration software and various activities in the fields of environmental engineering and socio-economic sciences by an interdisciplinary research team. More information can be found at the end of this article. Based on the interview guide, 18 interviews with public procurement professionals directly entrusted with the purchase of tyres and 4 additional expert interviews were conducted between between 17 December 2020 and 27 April 2021. All persons were selected and contacted directly. Three times, six interviews were conducted, of which each discussed: (a) large scale procurement processes of at least 1000 tyres per year or contract; (b) procurement situations of at least 100 tyres within 12 months; and (c) the procurement of up to 100 tyres annually. An additional four interviews were conducted with a person of overarching expertise, two persons who either purchase tyres as part of vehicle procurement or vehicle leasing and a fourth expert particularly experienced in sustainable procurement strategies. **Box 1. ** Topics of the interviews conducted with the public procurement professionals. * Procedures used for tyre procurement
* Software used for the procurement processes
* Decision criteria and indicators for the procurement of tyres
* Market analyses for the preparation of tenders
* Procurement of retreaded tyres
* United Nations Sustainable Development Goals and the Circular Economy Act in the procurement of car types
* Incentives that could stimulate the procurement of circular tyres
* Legal aspects
* Application scenarios for a tyre configuration software
* Priorities regarding a circular tyre value chain
* Information on the environmental and social performance of sustainable tyres
* Standards and labels/certification for sustainable tyres
* Request for further advice for the project
* Supplementary information on the organisations interviewed and their tyre pur-chasing volumes  
Table 1 provides details. One person answered in great detail in written form. For privacy reasons, this contribution is not presented separately but counted as an interview of \(\leq\)30 min. The interview material was analysed by applying the qualitative social research method 'content analysis'. Content analysis is a method for surveying social reality, in which characteristics of a manifest text are inferred from characteristics of a non-manifest context (taken from [44], p. 57, translated). As [45] describes, qualitative content analysis is characterised by its systematic approach to the analysis of linguistic material. A central technique of qualitative content analysis is structuring. The goal here is to filter out a certain structure from the material. [PERSON] [45] describes the following variants (translated):  
1. Formal structuring: wants to filter out the inner structure of the material according to certain formal structuring aspects. 2. Content structuring: wants to extract and summarise material on certain topics, on certain content areas. 3. Typifying structuring wants to find individual distinctive characteristics in the material on a typifying dimension and describe them in more detail. 4. Scaling structuring: wants to define characteristics in the form of scale points for individual dimensions and assess the material on this basis. As an example for a qualitative content analysis, [PERSON] [45] analyses interview-based material on'stress in the professional field'.