Reasonableness of a proposed System Theoretic Process Analysis (STPA) validation framework: An interview study

Since its inception, the STPA technique has gained increasing popularity among researchers and industry practitioners. Nevertheless, the validity of its application has not yet received much scientific attention. Although some informal validation approaches have been used by STPA users, no formalized validation framework has been elaborated for practical use. This paper investigates the reasonableness of the recently proposed STPA validation framework, which includes 15 validation tests, each focusing on a specific step of an STPA analysis. To do so, STPA experts in both academia and industry were interviewed. First, it is investigated what approaches they have been using for validating an STPA analysis, the findings of which were categorized and mapped with the proposed validation framework. This aims to investigate the similarities and dissimilarities between the theory-based validation framework and the informal methods applied by experts in current practice. Then, the proposed framework was presented to the interviewees to seek their judgments about its reasonableness. Feedback from practitioners indicated that the proposed STPA validation framework has certain strengths, while several opportunities exist for further improvement. In particular, the findings indicate that most of the proposed theory-based tests have been already used by STPA experts in an unstructured manner. The experts appreciated the framework in that it provides clear guidance on how to validate each step of an STPA analysis systematically, and found some additional theory-based tests interesting for consideration in practice. The results also suggest that further research is needed to develop systematic techniques for performing each test to facilitate its application by STPA experts.