A comparative case study involves analyzing similarities and differences across two or more cases that share a common goal. It involves collecting data over time from one or more organizations or groups within organizations. A comparative case study is built on four principles: theoretical sampling, triangulation, analytical pattern-matching logic, and analytical generalization. Theoretical sampling involves selecting cases determined by the research questions. Triangulation strengthens data by using different methods, such as interviewing respondents more than once. Analytical pattern-matching logic carefully links data to propositions.