> and they note only the fact that the _vehicle_ violated the speed limit. The _vehicle's owner_ gets a fine in the mail shortly after.
There, fixed that for you. Now, I'll admit, a large part of the time the owner is also the driver, but with speed cameras it is not the "driver" who receives the fine, but the _owner of the vehicle_.
The one difference with "speed cameras" and the NSA's data mining is that measurement of the rate of travel of a vehicle (assuming a properly calibrated and non-malfunctioning speed measurement device) is so close to 100% accurate as to be considered 100% accurate.
No "connect the dots, infer here, infer there" data mining in the NSA's dataset will ever be even within several orders of magnitude of accurate as compared to a properly functioning, properly calibrated, speed measurement device.
And that underlying, non zero, error rate is what triggers the base rate fallacy issue in statistical analysis. When an occurrence of X is extremely rare in a very large population without X, then the test for X has to be impossibly accurate for the results to not be swamped by false positives. And this is a completely counter intuitive result, which is why it is so often overlooked.
Pertinent quote from the Shiner article at https://www.schneier.com/blog/archives/2006/03/data_mining_f...:
"Let's look at some numbers. We'll be optimistic. We'll assume the system has a 1 in 100 false positive rate (99% accurate), and a 1 in 1,000 false negative rate (99.9% accurate).
Assume one trillion possible indicators to sift through: that's about ten events -- e-mails, phone calls, purchases, web surfings, whatever -- per person in the U.S. per day. Also assume that 10 of them are actually terrorists plotting.
This unrealistically-accurate system will generate one billion false alarms for every real terrorist plot it uncovers. Every day of every year, the police will have to investigate 27 million potential plots in order to find the one real terrorist plot per month. Raise that false-positive accuracy to an absurd 99.9999% and you're still chasing 2,750 false alarms per day -- but that will inevitably raise your false negatives, and you're going to miss some of those ten real plots.
This isn't anything new. In statistics, it's called the "base rate fallacy," and it applies in other domains as well. For example, even highly accurate medical tests are useless as diagnostic tools if the incidence of the disease is rare in the general population. Terrorist attacks are also rare, any "test" is going to result in an endless stream of false alarms."