Determining a risk factor in a low-validity environment is naturally characterized by subjective judgements. As soon as humans with variable and hardly identifiably expertise make decisions, they are in some way very likely influenced by cognitive biases. Biases are a deviation from rationality that limit rational argumentation and result from various circumstances. This work focuses on information, motivational and social biases. Information biases influence how information is gathered and evaluated. Motivational biases result from an interest in the result and the desire to manipulate risk parameters in a certain direction to influence the outcome. Social biases mainly result from group discussions, particularly if people are from different hierarchical levels and have powerful characters. The process has to make sure that a comprehensive understanding about project-related risks, including opinions and perspectives of all individuals involved, is reached. A careful elaboration of a ready-to-implement process, which ensures a highest possible objectivity, requires a careful analysis of the current process, of weaknesses of the process as well as the involvement of all stakeholders of the process. Several stakeholder-interviews and interviews with internal experts were conducted to gather a comprehensive picture of the actual situation and to identify improvement potentials. Furthermore, system-theory related considerations help to identify sub-systems and necessary interactions of these systems to ensure an optimal process flow. Finally, three possible process sequences are presented, whereas the first process includes the most comprehensive approaches for bias-mitigation, which leads to a clear preference of this process. Nevertheless, two less comprehensive alternatives are offered, which can be applied to less complex projects with lower project budgets. These alternatives allow a faster and less time-consuming determination of risk factors. All process steps are explained in detail and applied debiasing measures are highlighted. In case of a careful treatment of all process steps (especially for the first proposal) a well-founded, extensively objective risk factor can be handed over to management. By proofing the diligent execution of the process and the application of debiasing actions, acceptance in management should be improved and in the best-case approval of the proposed risk factor without further discussion is achieved.