For a survey to be truly anonymous you need to set up your survey so that you do not actually need to login to access it. This then means that anyone recording a set of answers has not identified themselves. For an anonymous survey, you should grant SEE, VIEW and RECORD rights to anonymous and get each respondent to refrain from logging in. The system will then store each set of responses against the anonymous user.
For other types of survey the identity of the user will be recognised by the system. This is appropriate for instance on a course feedback form. This is not released to the person setting up the questionnaire, although it may be possible for system administrators to identify particular respondents. There would need to be a very good legal case for system administrators to ever release these sort of details, so in general these questionnaires can be regarded as anonymous but restricted to certain users.
