There has been much speculation as to why the Thai military insist on using the GT200 pseudo-bomb-detector, when the Ministry of Science and Technology has run a test that proved it is ineffective. The device has since been disassembled to reveal that it is no more than an empty plastic box and a telescopic car aerial, and its ‘pre-programmed cards’ are un-programmable bits of laminated paper.

The explanations for this military intransigence range from an understandable reluctance to own up to mistakes that have cost lives, limbs, liberty and a whole lot of government money, to a rigid military mentality that exists within its own heavily circumscribed worldview and is not susceptible to alteration by anything as flimsy and insubstantial as facts.

I think the answer to the question may in fact lie in the way Thais are educated. Or more precisely, how they are tested during their education.

First of all, it should be noted that it not just the military that seems to have serious epistemological problems with evaluating evidence. Khunying Dr Pornthip Rojanasunand, Director of the Central Institute of Forensic, er, Science, said the device was effective, and, after the trials showed otherwise, said it was ‘not a scientific piece of equipment’ but it worked well enough for her office to continue using it.

Her boss, Justice Minister Pirapan Salirathavibhaga (with legal degrees from Thailand and the US), took a few moments away from his Ministry’s self-appointed most important task of defending the institution to note: ‘The suspicious point is that if the GT200 device does not work and is of no quality then this device would be unable to detect any bombs, but in the test it was able to detect the bombs 4 times, but not in 16 instances.’

Let’s apply the Minister’s logic to student Somchai who has just taken a 100-item multiple-choice test (with the standard 4 choices per question) in, well, any subject you care to name. The Thai educational system has a very robust faith in the multiple-choice format and thinks it can be used to test anything from theoretical physics to Keep Fit 101.

Somchai is a bit of a goof-off and has spent his term strumming his fingers to the bone, practicing the raising of coloured bits of cardboard among hundreds of others doing the same, and wondering at great length, without any great success, how to get inside the kickers of a rather cute cheerleader. But he’s done no studying.

So when faced with the test, he does what all such students do – he shuts his eyes and guesses.

Now Minister Pirapan will expect this know-nothing non-student to get exactly zero. If he gets even one answer correct, it will be ‘suspicious’. It would, to the Minsters’ way of thinking, prove that Somchai does know something.

Perhaps the Minister should be introduced to the concept of ‘chance’.

Somchai could get zero because he knows nothing. He could also get 100% correct under exactly the same conditions of ignorance, though both results are statistically very unlikely. For each question, Somchai has a one-in-four chance of getting the right answer without knowing that it is the right answer.

Just like the GT200 in the Ministry of Science and Technology’s test. In each round it had to identify which box of four contained the explosive. Even if it was just an empty plastic box (which it is) it had a one-in-four chance of picking the right box each time.

Now for Somchai on his 100-item test, blind ignorance will most likely (but not necessarily) yield him a score of 25. Out of the 20 tests for the GT200, the most likely result for a piece of garbage is 5 correct identifications.

And they are equally meaningless as measures of Somchai’s knowledge (which is zero) and of the GT200’s efficiency (also zero).

Now in the case of Somchai, there is a simple method to discourage ignorant guessing. Instead of counting a correct answer as 1 and either an incorrect answer or no answer as zero, you give an incorrect answer a score of minus 1/3. (No answer still gets zero.)

The statistically most likely result for a compulsive but ignorant guesser would be 25 correct and 75 incorrect, i.e. 25 minus 75/3, or zero.

This method (which must be communicated to the test-taker in advance) discourages blind guessing.

If we applied it to the GT200 test, we would get plus 4 for the 4 lucky shots and minus 16/3 for the misses. A net score of minus 1 and one third. Which I hope the Minister does not find suspicious and accepts as a clear indication that his Ministry has,suspiciously, spent millions of taxpayers’ baht for nothing.

However, the ‘minus for wrong answers’ wheeze only works if Somchai knows about it ahead of time and takes it into consideration in deciding, for each question, whether to guess or just not answer. Somchai can do this because Somchai has a brain.

The GT200 has no brain. One is tempted to reach the same conclusion about the people who insist on using it.

About author: Bangkokians with long memories may remember his irreverent column in The Nation in the 1980's. During his period of enforced silence since then, he was variously reported as participating in a 999-day meditation retreat in a hill-top monastery in Mae Hong Son (he gave up after 998 days), as the Special Rapporteur for Satire of the UN High Commission for Human Rights, and as understudy for the male lead in the long-running ‘Pussies -not the Musical' at the Neasden International Palladium (formerly Park Lane Empire).