In the United States National Science Foundation and the National Institutes of Health have mandated training STEM doctoral students in the ethical and responsible conduct of research to improve doctoral students' ethical decision-making skills; however, little is known about the process and factors that STEM faculty and graduate students use in their decision-making. This exploratory case study examined how four triads of chemistry faculty and their doctoral students recruited from three research universities in the eastern United States engaged in ethical (...) decision-making on issues of authorship, assignment of credit, and plagiarism. A mixed-methods approach involving the administration of an online survey consisting of three open-ended case studies followed by a think-aloud interview was utilized. Participants were found to use analogical reasoning and base their decision-making on a common core set of considerations including fundamental principles, social contracts, consequences, and discussion with an advisor, often using prior personal experiences as sources. Co-authorship did not appear to impact the doctoral students' ethical decision-making. Gender may play a role in graduate students' decision-making; female doctoral students appeared to be less likely to consider prior experiences when evaluating the vignettes. Graduate students' lack of knowledge of the core issues in the responsible conduct of research, coupled with their lack of research experience, and inability to identify the core considerations may lead them to make bad judgments in specific situations. Our findings help explain the minimal impact that the current responsible conduct of research training methods has had on graduate students' ethical decision-making and should lead to the development of more effective approaches. (shrink)