Data Protection & Freedom of Information Office

The distinction between anonymous and pseudonymous data is very important in data protection legislation.

• Truly anonymous data is not considered personal data, and is therefore not subject to data protection legislation.
• Pseudonymous data, while not immediately identifiable, is personal data and is subject to data protection legislation.

But what is the difference, in practical terms?

Anonymous data

Anonymous data is information which does not allow the identification of any individuals associated with that data. If your data is fully anonymised, it will have no identifiers or links that might allow anyone (within or without the University) to directly or indirectly identify associated individuals. 

Simply removing (or not collecting) a name does not make data anonymous 

Email addresses, identification numbers, online identifiers, etc, are all specific to one individual and can identify them without being directly associated with their name. Additionally, if you have multiple data types, it may be possible to combine them in to one identifiable picture.

For example:

• If you are working with age, gender, course of study, and nationality that may narrow the population enough to enable identification of one particular student and you would therefore not be able to treat your dataset as anonymous

Pseudonymous data

Pseudonymous data is information that has been altered, changed, or held in such a way that it does not immediately enable identification of any individual person. However, when data is considered pseudonymous, it means additional information is held by the organisation or by other individuals that allows for potential identification of individuals related to that data. 

Pseudonymous data is classed as personal data under data protection legislation and is subject to that legislation

For example:

• You hold a spreadsheet that lists course modules, students' marks on those modules, and alphanumeric identifiers associated with the students. You aren't able to identify any individual student on the spreadsheet. However, your colleague holds an additional spreadsheet that links your alphanumeric identifiers to specific student names.

If you combined the two spreadsheets, you would be able to identify the students on your spreadsheet. This makes your data pseudonymous, rather than anonymous (fully unidentifiable) data.