This dataset comprises the structured coding frameworks and comparative content analysis matrices generated during a study of Patient Safety Incident Investigation (PSII) reports within mental healthcare services. The research evaluates the transition from traditional Root Cause Analysis (RCA) toward modern Systems Thinking frameworks. Because the source materials consist of highly confidential institutional patient safety incident records, the raw reports and complete internal text analyses are withheld to protect the legal anonymity of services and individuals. Summary analytical findings and frameworks are fully detailed in the associated publication: Bifarin et al. (2026) From Root Cause Analysis to Systems Thinking: A Comparative Content Analysis of Patient Safety Incident Investigation Reports in Mental Healthcare, Journal of Evaluation in Clinical Practice.