One problem with the nothing-to-hide argument is that it assumes innocent people will be exonerated certainly and effortlessly. That is, it assumes that there are no errors, or if there are, they are resolved quickly and easily.<\/p>\n
Suppose the probability of a correctly analyzing an email or phone call is not 100% but 99.99%. In other words, there\u2019s one chance in 10,000 of an innocent message being incriminating. Imagine authorities analyzing one message each from 300,000,000 people, roughly the population of the United States. Then around 30,000 innocent people will have some \u2018splaining to do. They will have to interrupt their dinner to answer questions from an agent knocking on their door, or maybe they\u2019ll spend a few weeks in custody. If the legal system is 99.99% reliable, then three of them will go to prison.<\/p>\n
Now suppose false positives are really rare, one in a million. If you analyze 100 messages from each person rather than just one, you\u2019re approximately back to the scenario above.<\/p>\n
Scientists call indiscriminately looking through large amounts of data \u201ca fishing expedition\u201d or \u201cdata dredging.\u201d One way to mitigate the problem of massive false positives from data dredging is to demand a hypothesis: before you look through the data, say what you\u2019re hoping to prove and why you think it\u2019s plausible.<\/p>\n
The legal analog of a plausible hypothesis is a search warrant. In statistical terms, \u201cprobable cause\u201d is a judge\u2019s estimation that the prior probability of a hypothesis is moderately high. Requiring scientists to have a hypothesis and requiring law enforcement to have a search warrant both dramatically reduce the number of false positives.<\/p>\n
Related: You do too have something to hide<\/p>\n