This passed on from a SysAdmin, let’s call her MaryAnn, from the EFF: A Primer on Information Theory and Privacy.
Excerpt:
If we ask whether a fact about a person identifies that person, it turns out that the answer isn’t simply yes or no. If all I know about a person is their ZIP code, I don’t know who they are. If all I know is their date of birth, I don’t know who they are. If all I know is their gender, I don’t know who they are. But it turns out that if I know these three things about a person, I could probably deduce their identity! Each of the facts is partially identifying.
Go take a look if only to consider the Math.