# Multidimensional Study on Users' Evaluation of the KRAKEN Personal Data Sharing Platform
## 2 Methods  
In Autumn 2021, we conducted a two-phase evaluation of the KRAKEN prototype by involving an overall sample of 15 participants. Each participant was asked, first, to individually access and use the prototype to assess its usability. The prototyped data sharing platform was composed by a Self-Sovereign Identity (SSI) mobile application required to access the KRAKEN data-sharing marketplace, populated with sample data products in the health and education piloting domains. Participants were asked to perform a set of key tasks representing the main functionalities supported by the prototype and to fill in a digital version of the System Usability Scale (SUS) questionnaire [19] to assess its usability. Examples of tasks performed by participants involved in the health pilot evaluation were registering to the KRAKEN marketplace by means of the KRAKEN SSI mobile app, browsing the available products in the health sector, requesting access to a data product, and offering access to a data product by setting the relevant privacy options to access it. Examples of tasks performed by participants involved in the education pilot evaluation were logging in to the education connector, connecting the wallet app to the education connector, exporting a credential (grade or diploma) into the mobile wallet, displaying the credential in the wallet on the web-based marketplace, registering to the KRAKEN marketplace, accessing/browsing the available data products, and updating the user profile. After the usability assessment, participants were invited to join an online group interview (duration 1.5 h each) to further report about their expectations, preferences, and concerns regarding the KRAKEN solution tested. A total of 4 group interviews were carried out, 3 for the health pilot evaluation (attended by 12 participants) and 1 for the education pilot evaluation (3 participants), each moderated by a researcher with expertise in Human-Computer Interaction and video-recorded to enable a more detailed analysis of participants' responses. The moderator, initially, provided a brief introduction to the interview objectives. Then, participants were asked to answer a series of semi-structured questions regarding their expectations, preferences, ethics concerns, and intention to use the KRAKEN data sharing platform. Table 1 shows the list of topics and questions posed to participants involved in the health pilot evaluation, while Table 2 shows the list of topics and questions posed to participants involved in the education pilot evaluation. Group interviews or focus groups are suitable for a more in-depth investigation of users' attitudes and preferences toward new technological solutions, since open-ended discussions with users can help researchers to better understand the issues and concerns related to the possible future adoption of these solutions [20]. The recruitment of participants was based on personal contacts of partners in the KRAKEN consortium, selected based on representativeness of the key target user groups addressed by the KRAKEN solution. The key target user groups were identified in the initial design phase of the project by means of research and market analysis activities to develop the relevant use case scenarios for both the health and education pilot domains. As an example, in the health pilot domain, the main target user groups identified in the categories of data providers and data consumers were: researchers managing projects in the area of big data, blockchain technologies and digital health solutions on behalf of research centers/institutions, managers or representatives of private companies working at the development of digital health solutions, and project managers working in public health projects and solutions. In the education pilot domain, the main target user group for data providers was represented by university students enrolled at the Technical University of Graz (TUGraz, Austria), partner of the KRAKEN project and leading the development of the KRAKEN education pilot.