The Power of Twelve


STR Column by Jim Davies, published on April 18, 2004

In a zero-government society (ZGS) the only disputes that could arise would be those between individuals in society, and not between individuals and government--for there wouldn't be one. And those disputes would be settled under the terms of contracts previously agreed, as is sometimes done today in civil contracts; e.g. that a certain arbitration service shall be used in the event of dispute arising under its terms.

Consequently, I'm not sure that the institution of the jury would be much in demand. It's certainly possible that a contract might specify that disputes will be resolved by a panel of 12 individuals invited at random from society and paid by the losing party for their services; but I suppose a smaller panel of experts in the field would generally be preferred.

Meanwhile, we don't have a ZGS, alas, and so the environment is very different.  In addition to disputes between individual members of society there exist disputes between members and the "great fiction" of government. Those disputes are often called "crimes", and involve allegations of breaking "laws"--which are neither more nor less than oxymoronic, one-sided contracts. And in that environment, juries play a vital role.

That role, from AD 1215 onwards, has been to limit the power of government.  It's a modest objective to be sure - but worthwhile, surely. The first English juries under the Norman regime acquired the power to negate (nullify) His Majesty's decrees. Since then, government has been less than absolute and the choice of 12 as an appropriate size was remarkably happy.

All other players in today's courtrooms are paid or licensed by the government. Even the "defense counsel", apparently representing the interests of his client the defendant, is actually an "officer of the court", with an obligation to keep the rules of the judiciary or lose his license to practice Law. Government has a tight lock on what it pleases to call "Justice" - with one exception: the jury. And they are working hard to bend juries to their will; by questioning each in the jury pool so as to select a panel likely to convict, and even by 
punishing a juror who dares to "nullify" the law.

Yet to nullify laws is exactly why the English peers of 1215 created juries.

The jury's independent power over the particular law as it applies to a particular case is absolute and unquestionable, which is why government hates juries so much. This "nullification" was what brought down Prohibition; one clearly-guilty defendant after another was acquitted, so the law became unenforceable and so was repealed. It's worth looking at the math.

Suppose there is a law that is popular with 90% of potential jurors, but regarded as intrusive and wrong by the remaining 10%. Suppose also that a jury is selected randomly from that pool, properly aware that they can acquit on the grounds that it's a bad law if they want to. What is the probability of conviction?

The answer is not 0.9 or 90%. The answer, in mathematics, requires one to multiply the individual probabilities that any one juror will vote to convict. That is, 0.9 by 0.9 by 0.9 . . . 12 times. Or, 0.9 to the power of 12.

Try it on your calculator: the answer is 0.282, i.e. a 28.2% probability of conviction! For breaking a law that 90% of voters like!

No ambitious prosecutor would even bring the case.

Here's a table of how other probabilities work out. The left-hand column is an expression of how many in a population support the particular law; the right hand column shows the probability that a fully informed and randomly selected jury of 12 will convict under it, regardless of the facts of the case--likewise expressed as a percentage

% Support Conviction Rate
100 100
99 88.6
98 78.5
97 69.4
96 61.3
95 54.0
94 47.6

The astonishing Power of Twelve is that unless a law is popular with at least 95% of a jury pool, a prosecutor has a less than half probability of winning his case, and that to enjoy better than a 75% chance of victory the subject law must face no more than 2% dissenters in society! 

Juries may not, alas, be able to bring down governments altogether and create a ZGS.  But in the meantime, they can provide an extraordinarily powerful constraint.

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