I can't recall any diagnostic test in modern medical history, however, that produced 20,000 false positive results and no true positives. I think for a test like that you have to go back to the pre-rational era.
The pre-rational era in which Homeland Security lives today:
I've written about this before, often reacting to Schneier's prior posts:The Justice Department's proposed budget for 2008 reveals for the first time how often names match against the database, reporting that there were 19,967 "positive matches" in 2006. The TSC had expected to match a far fewer number 14,780. The watch list matched people 5,396 and 15,730 times in 2004 and 2005 respectively.
The report defines a positive match as "one in which an encountered individual is positively matched with an identity in the Terrorist Screening Data Base, or TSDB."..
How do I know they're all false alarms? Because this administration makes a press splash with every arrest, no matter how scant the evidence is. Do you really think they would pass up a chance to tout how good the watch list is?