Mixed-method observational study: the impact of pandemic related changes in healthcare onquality of life and experiences with healthcare in Dutch patients undergoing surgery oranother intervention during the covid pandemic (2020-2021).Phase 1: qualitative study to gain insight in relevant themes in Patient ReportedExperiences Measures (PREMs) by conducting focus groups Phase 2: creating and validatinga questionnaire based on themes identified in phase 1 Phase 3: questionnaire study amongDutch patients who underwent an intervention in 2020-2021 using the validatedquestionnaire of phase 2. The answers will be linked to data from national patientsregistries in surgery, cardiology, orthopedics and neurology.