A case study is an intensive and documented research project on a population, scenario, or group. They may contain qualitative and/or quantitative research. You can organize your subjects multiple ways, and are limited to the five hat racks: categorically (by similarity or relatedness) [i.e Graves], time (chronologically) [Brandt], location (position) [Hayes], alphabet, and continuum.
Data is collected and organized in many different methods. Surveys, recordings, observations, opinions, oral discourse, written discourse, and through conversations and de/briefings. If the researcher has a defined hypothesis or theory, the research trends can be compared in some way. The idea of development and code come into play during the analysis.
Generalizations can be made based on the purpose of the research. If hard evidence and trends are demanded, then a well-documented and tested study needs to be completed. Studies are usually generalized though and typically state that future research may be required. Yet, some research may be composed of many case studies to present an argument.