The Information That Is Needed to Identify You: 33 Bits
4th August 2010
How many pieces of information are needed to identify an individual? In the field of re-identification science, it’s 33 “bits,” specifically “33 bits of entropy.” (Information-science researchers refer to random pieces of information as “entropy.”)
Why 33? Because a “bit” is computer lingo for an on-off switch that can have only two values, 0 or 1. And 2 multiplied by itself 33 times is a bit more than the number of people on earth — 6.6 billion. Two to the 32nd power is lower than the world’s population. So, in theory, it takes at least 33 “bits” of information to uniquely identify someone.
Each piece of information you add reduces the pool of possible individuals. But not every data point is worth the same number of “bits.”