One of my mentees and I will be presenting at conference this fall (more on that later). We began discussing their dissertation study and the issue of scope creeping. The problem statement is perhaps the most important concept to understand and acquire as a researcher. Learning how to avoid scope creep is part of that.
I first heard about scope creeping from Dr. Holly Rick at my first doctoral residency. She explained that too often students will try to address a problem too broadly - or rather, the problem they identify is too broad to effectively design a research study.
Picture it like an hourglass: the background of the study is broad (establishes the environment in which a problem exists). The research problem identified is specific, concise, and addresses one facet of a greater issue. The study that you conduct exists within the scope of the problem. However, once the study findings are disseminated, they can potentially be applied back to the larger phenomenon which exists. In fact, a thorough discussion of findings would include the implications of those findings on professionals, scholars, society, etc.
Scope creep can be identified through editing, reflection, peer review, and practice.