Deidentification: Anonymous vs Pseudonymous and Identifiers
When data cannot be traced to a person, privacy law no longer applies. Anonymization removes identifiability; pseudonymization masks identity with a unique identifier. EU law treats pseudonymized data as personal under the GDPR, but anonymized data falls outside it. Identifiers range from strong identifiers to quasi-identifiers.
How this supports CIPP/US study
Use this lesson to identify the legal source, actor, data and activity before applying a rule to a scenario. Continue with the CIPP/US study guide.
Privacy laws apply to personal data; when data can no longer be traced to a person, they no longer apply. Anonymization removes identifiability, while pseudonymization masks identity behind a unique identifier (e.g. 'Patient 13579'). EU law treats pseudonymized information as personal data under the GDPR, in contrast to anonymized data, which falls outside the GDPR.
| Identifier | Example / nature |
|---|---|
| Strong identifier | Social Security or passport number; clearly identifying |
| Weak identifier | Must be combined with other information to identify |
| Quasi-identifier | Date of birth - over 25,000 cells (366 days x 80+ years) make it highly identifying when combined with external knowledge |
FTC Chair Ramirez (2016): data is personally identifiable when it can be reasonably linked to a particular person, computer, or device - including persistent identifiers like device IDs, MAC addresses, static IPs, and loyalty card numbers. Linked data already ties to identity; linkable data could be tied to it.
Key terms - quick answers
What is “Anonymization”?
What is “Pseudonymization”?
What is “Deidentified”?
What is “Strong identifier”?
Sources and study method
This independent lesson uses active recall, spaced retrieval and scenario practice. Read the full study method.