When the sample is bound to professional secrecy
If the sample consists of persons who are bound to observe professional secrecy (e.g. healthcare professionals, teachers, etc.), the interview guide or questionnaire must be designed in such a way that respondents can express their views on the various issues notwithstanding their professional secrecy.
In addition, it is often appropriate to remind the participants that if they are to mention any patients/students, they must exclude both names as well as any indirect personally identifiable information (institution, dates, specific diagnoses/events, etc.). In student projects, the supervisor has a particular responsibility to ensure that the student does not treat confidential information.
Processing confidential information may only take place either after obtaining consent from the person concerned or after receiving an exemption from the appropriate authority.