Anonymous data are recorded so that the information can never be linked to the subject who supplied it.
Confidential data are recorded so that the information is not immediately identified with the subject who supplied it, but such a link is possible. Confidential data are usually coded–that is, the subject is assigned a unique identifier that will be used to identify the data. The code identifies the data and the subject's identity is kept separate from the code and data. Coded data are not anonymous.