You hate to take a “What, me worry?” attitude towards any aspect of the war on terrorism, but it’s hard to get too worked up over the results of a study, released recently by the Transportation Security Administration, which found that screeners at airport checkpoints failed to detect one in four weapons carried by undercover testers.

Why?

Because the study did not take into account the demographics of the undercover testers.

What we know about international terrorism, at least so far, is that the threat comes from two relatively recognizable groups: (1) Middle-Eastern males; (2) fidgety dupes who have fallen in with Middle-Eastern males.

So how many of the undercover testers used in the TSA study fit either profile? The fact that a quarter of the weapons slipped past screeners, in other words, begs several questions: How many of the weapons that got through were actually carried by guys named Ahmed, Mohammed or Nasir? How many were carried by guys who paid for their tickets in cash? How many by guys who bought one-way tickets? How many by guys who were sweating profusely? How many by guys who were muttering to themselves?

The case can be made, of course, that if even an elderly grandmother from Kansas manages to board a 747 with a nail clipper, the screener who allowed her to pass has screwed up. But if the screener’s attention was distracted at that moment by the passenger behind her, the swarthy guy kissing the Koran and glancing nervously side to side, I’d be reluctant to fault his priorities. The truth is that an elderly grandmother with a nail clipper poses a negligible security risk; in fact, I’d be willing to declare an immediate immunity for elderly grandmothers who board planes with nail clippers.

The fact that one out of four weapons were slipped past screeners is, in the final analysis, only significant if the study replicates real world conditions. If, on the contrary, the study is premised on the liberal lie — and that’s what it is — that terrorists come from a random cross section of humanity, then the results are meaningless. They may even be worse than meaningless if they are used against the screeners; indeed, punishing screeners for failing to pretend that terrorists crop up equally among every demographic will likely cause them to adopt the pretense thereafter. And if training screeners means instructing them to scrutinize all passengers equally, to ignore their altogether natural inclinations to stereotype terrorists according to ethnic, gender, age and behavioral markers, then the rest of us would be better off with untrained screeners.

This is, in a sense, a rerun of the propaganda of the AIDS crisis. The media’s insistence that AIDS was an egalitarian threat, that it was as likely, for example, to strike heterosexuals as homosexuals, succeeded only in diverting finite resources away from the high-risk community and towards the low-risk community. (And, no, for those readers who are ritually disposed to read between the lines, I did not just compare AIDS victims to terrorists.) Deciding policy based on how we’d like the world to be, rather than on how the world actually is, inevitably leads to self-defeating policy.

Maybe, in the future, the Transportation Security Administration will conduct a study that accurately reflects what we know about the demographics of terrorists — rather than maintaining the pretense that terrorism is an equal-opportunity enterprise. Until then, it can spare us the alarmist results.