Main research questions are “how” or “why” questions. All case studies rely on multiple sources of evidence and benefit from the prior development of theoretical propositions and hypotheses , ,. Case study method a variety of tools are made available for student examination, use and critique. For example, a mathematician trying to formulate a model to solve the queuing problem in an airport may conduct existing research in similar areas. Descriptive studies are used to analyze a certain sequence of events, which happen sometime in the past.