One of the outgrowths of the digitization and mass collection of personal information is the ability to match disparate bits of data into a profile of individual, a profile that can then be used to make certain judgments about that person. Privacy considerations aside for a moment, when it works it is tremendously powerful. But when the data quality is poor or matching algorithm is flawed… It might mean sending a coupon to the wrong “jane smith” or maybe keeping air marshals from the flight they’re meant to patrol.

http://www.economist.com/blogs/gulliver/2008/05/that_pesky_nofly_list.cfm