Task complexity as a performance shaping factor: A review and recommendations in Standardized Plant Analysis Risk-Human Reliability Analysis (SPAR-H) adaption

•This is a contribution to the development of the PetroHRA method.•Fifty-three research articles, review articles and academic books were reviewed.•An objective perspective of complexity is chosen.•A “Task Complexity” PSF is proposed with six complexity categories.•The complexity categories are: goal, size, step, dynamic, structure and connection.