There they go again worrying about the wrong things!

Matthew Yglesias writes:

Spencer Ackerman tries to problematize the conclusion that the underpants bomber incident really represents a grievous intelligence failure. You should read his whole analysis. But in brief, while by definition letting a bomber on an airplane is a failure, based on what was actually known about Abdulmutallab, excluding him from flying would involve erecting pretty substantial barriers to entering the United States in ways that would have real costs. As I said before, the key point about identifying al-Qaeda operatives is that there are extremely few al-Qaeda operatives so (by Bayes’ theorem) any method you employ of identifying al-Qaeda operatives is going to mostly reveal false positives.

Looking at it one way, he is right. Looking at it another way, he is quite wrong.

• Any simple, affordable screening method that seeks to unfailingly identify anyone among nearly seven billion people who would create a specific type of crime anytime and anywhere is bound to fail to achieve that hugely unreasonable goal.
• I think the number of false positives among people who are convicted in the courts of attempted terrorist acts is very small indeed.

In fact screening is generally a sequential process. Simply saying that we are seeking Al Qaeda operatives is itself a screening step. Screening for Al Qaeda operatives is unlikely to identify another Oklahoma City bomber or serial killer. We screen lots of people with simple tools giving lots of false positives, and put them on a watch list. We screen the smaller number of people who ask for U.S. visas more carefully. Those who do receive visas are screened still more carefully for explosives and weapons when they seek to board an airplane. If charged with a crime, they should be investigated very thoroughly indeed. Ultimately, before finding a person guilty, prosecutors will have to decide that there is enough evidence to bring the person to trial, a judge will have to decide that the investigation and presentation of evidence has been fair, and a jury will have to decide if the case has been made beyond a reasonable doubt.

The point is, screening is a sequential process with more expensive and more accurate processes being applied following prescreening with simpler cheaper processes. Think about medical screening where one goes through a physicians office visit and stages of clinical laboratory work -- chest x-ray followed by CT scan and then by exploratory surgery -- before a final diagnosis is made.

The more fundamental point is that we are probably doing a poor job of risk analysis, spending too much money to avoid relatively small risks and too little money to avoid relatively large risks. We probably worry too much about Al Qaeda and too little about traffic accidents, communicable diseases, and behavior that creates risks of non-communicable disease such as cardio-vascular disease and cancer. The publicity that attends a failed attack to blow up an airplane dwarfs that which attends the thousands of deaths a year from flu, not to mention heart attacks, strokes and cancer. So our political leaders pander to public opinion with new programs to prevent the uncommon, ignoring the more common risks!