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This is a footnote to the main video about mathematically protecting the privacy of individuals
when you’re publishing statistics from a private dataset, like a medical study, or
a census, or whatever.
There are in fact two kinds of privacy violation that can happen from a survey, and they’re
qualitatively very different from each other.
The first kind is the direct breach of the privacy of an individual by somehow revealing
private information specific to them (like their birthday, or blood type, or Harry Potter
house), and this is the kind of privacy violation the main video focused on.
The second kind is an indirect violation of privacy via association with a group (like
how men are more likely to be overpaid, or how Slytherins are more likely to be evil,
or how overpaid men are more likely to be Slytherins…).
Of course, revealing trend-based information about a group is precisely the purpose of
doing surveys; we, as a society, want to know the expected lifespan of smokers vs non-smokers,
or the typical month in which professional hockey players are born.
But if a survey reveals that hockey players are more likely to have January birthdays,
then knowing somebody plays in the NHL gives you insight into a supposedly private piece
of information, and does so regardless of whether or not that player themselves participated
in the survey!
If we wanted to protect the privacy of individuals 100%, pretty much the only option would be
to outright prohibit all studies and surveys that use any individual information, whatsoever.
But then we couldn’t have representative democracies, or study diseases, or keep an
eye out for dark wizards coming out of Slytherin, or lots of other useful things.
So if you are going to do a study, the best you can do is to not violate any participant’s
privacy more than their privacy would have been violated if they hadn’t participated
in the study.
That is, the current wisdom is that it’s ok to reveal that NHL players are more likely
to have January birthdays , but it’s not ok to reveal the birthday of a specific player.
And of course, you’d have to reveal the January birthdays fact using a mathematically
guaranteed privacy protection… but that’s what the main video is about.
And if you want to ensure you don’t have online information specific to you stolen
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