Why the TSA is, and always will be, an enormous waste.
"The base rate fallacy is the failure to account for underlying incidence of the condition being tested for. Imagine this hypothetical (and completely fantastical) scenario: that the TSA employs a near-perfect test for risk-based screening, a test that always flags terrorists if they are present and only flags innocent people 1 time out of 10,000. (The TSA’s actual success rate at flagging known terrorists is zero.)
Under these conditions, only one out of every five million people flagged would be a terrorist. This is the base rate fallacy in operation. In other words, for all intents and purposes, every flagged person is a false positive.
A screener doesn’t handle five million flagged passengers in an entire lifetime. That means that screeners and methods will be biased — even designed — to conclude that all positives are false positives.
If an actual terrorist got flagged in a system like that, he would be dismissed as some sort of false positive. The false positives aren’t just a waste of time and money — they undermine the entire system, because handling so many false positives will alter the thinking of the people operating the system.
It simply cannot work to use universal screening on any population where the incidence of what you’re screening for is less than one in a billion; it’s impossible. No demographic category of airline passengers has a large enough incidence of terrorism to be useful as a 'risk-based-screening' subgroup."
https://web.archive.org/web/20170401033419/http://tsanewsblog.com/3271/news/base-rate-fallacy-dooms-tsas-risk-based-screening/
"The base rate fallacy is the failure to account for underlying incidence of the condition being tested for. Imagine this hypothetical (and completely fantastical) scenario: that the TSA employs a near-perfect test for risk-based screening, a test that always flags terrorists if they are present and only flags innocent people 1 time out of 10,000. (The TSA’s actual success rate at flagging known terrorists is zero.)
Under these conditions, only one out of every five million people flagged would be a terrorist. This is the base rate fallacy in operation. In other words, for all intents and purposes, every flagged person is a false positive.
A screener doesn’t handle five million flagged passengers in an entire lifetime. That means that screeners and methods will be biased — even designed — to conclude that all positives are false positives.
If an actual terrorist got flagged in a system like that, he would be dismissed as some sort of false positive. The false positives aren’t just a waste of time and money — they undermine the entire system, because handling so many false positives will alter the thinking of the people operating the system.
It simply cannot work to use universal screening on any population where the incidence of what you’re screening for is less than one in a billion; it’s impossible. No demographic category of airline passengers has a large enough incidence of terrorism to be useful as a 'risk-based-screening' subgroup."
https://web.archive.org/web/20170401033419/http://tsanewsblog.com/3271/news/base-rate-fallacy-dooms-tsas-risk-based-screening/