John Allen Paulos in his always brilliant Who’s Counting column at ABC News:
Even if the probability that the purported terrorist profile is accurate were an astonishing 99 percent (if someone has terrorist ties, the profile will pick him or her out 99 percent of the time, and, for ease of computation, if someone does not have such ties, the profile will pick him or her out only 1 percent of the time), most of the hits would be false positives.
For illustration, let’s further assume that one out of a million American residents has terrorist ties — that’s approximately 300 people — and the profile will pick out 99 percent, or 297 of them. Great. But what of the approximately 300 million innocent Americans? The profile will also pick out 1 percent of them, “only” 3 million false positives, innocent people who will be caught up in a Kafkaesque dragnet.
It should be reiterated that such broad scale wiretapping and data mining is not only of questionable legality if not downright unconstitutional, but it is also ineffective and a waste of resources. Terrorism is a problem, but so are handguns, health care, the deficit, the environment, education, and a host of other issues that are more important to our personal and, I think, our national security.
More here.