This online appendix provides the materials of an experiment regarding the performance of individual subjects (24 students) in the extraction of conceptual models from a specification expressed: [IV1] as user stories or use cases [IV2] for one of three types of fictitious systems: hospital management system, urban traffic simulator, and international football association portal We measure the performance in terms of validity (DV1) and completeness (DV2) against models that were created by domain experts (the three authors of the paper and of this online appendix) from each of the specifications. The materials include The description of the three systems (folder System Descriptions) An Excel spreadsheet that includes raw data, charts, and statistical results The guidelines that the authors used in assessing the quality of the subjects' models against the expert models For each student who participated in the experiment and gave consent, The specification, either via user stories or use cases, created by the student The student model created by the student The expert model created by one of the paper authors Note that these files are highlighted to denote how we applied the tagging guidelines