First, what are they and why does it matter?

If Firas wanted to know what proportion of MDS students have Type A personalities, he could give a personality quiz to everyone in class and tally up the results. But if the classroom cleaner stole the pile of completed quizzes, they could figure out which quiz belonged to a particular student and maybe even sell that person’s quiz to a company targeting data science students. Well, we definitely don’t want that to happen!