Try again. The full name of a person will identify him / her directly. This is the strongest identifier out of all options.

Try again. Hospital number, like any identification card numbers, is specific to an individual. Therefore, it is a direct identifier.

Try again. Addresses (email address, internet IP address, home address) and telephone numbers are only used by one or very few individuals, thus, are rather specific identifiers.

Try again. A full-face photograph would identify a subject directly. A close-up photograph of a small mole on the chest will be less identifying than a close-up photo of an unusually large or hairy mole on the cheek.

Try again. Voice, like fingerprints, retinal patterns and genetic codes, are all specific to an individual and can be used in biometric identification.

Correct. Gender, like ethnicity, is quite general on its own. However, this might not be the case if there are very few people from a gender or ethnicity (e.g. transgender or Asian-Hispanic mix).

Try again. Date of birth is a rather specific identifier, it is not shared by many people. ‘1 Jan 1940’ is a stronger identifier than ‘1940’.

Try again. The combination of all three makes a stronger identifier than when each is presented singly.

Try again. When any records are dated, it makes identification much easier. This is even more so if someone had an abnormal record (e.g. 40 beats per minute).

Try again. Although anonymised, a simple web search would enable you to identify the author of a Twitter post immediately. ⁽¹⁾ Try and identify who wrote this post.

Click here to read the ethical and methodological challenges that a team of researchers faced when using Twitter’s data to study about infectious disease outbreak. ⁽²⁾