The Rule of 11

Related Link » Professor Charged in Ala. Shooting Killed Brother in 1986
“HUNTSVILLE, Ala. — More than 23 years before a college professor was accused of shooting six of her colleagues at an Alabama university, her teenage brother died from the blast of a shotgun she held in the kitchen of her family's home in Massachusetts.”
— Sunday, February 14, 2010 (AP)

Our Anglo-American justice system is predicated on a long history of jurisprudence, stemming from fundamental concepts such as "innocent until proven guilty", "beyond reasonable doubt", "unanimous verdict for conviction", and "better to acquit X ( > 1 ) guilty defendants than to convict 1 innocent defendant". It is certainly not a perfect system, for there exists documentation, which proves (after the fact) that cases of mistaken verdict do occur from time to time, in accordance with intentionally preferential safeguards for the innocent. Nevertheless, as with any real-world solutions to real-world problems, it is arguably a better justice system than any other codified by civilized society.

Suppose, however, we wanted to improve the accuracy of expected verdicts? Specifically, we might wish to increase the conviction rate of the guilty, without unduly increasing the (erroneous) conviction rate of the innocent. How might we accomplish such an improvement, without altering any fundamental concepts of our justice system?

Consider the possibility of reducing the jury size from 12 to 11 jurors. Such a decremental (as opposed to incremental) change would constitute nothing more than a quantitative (as opposed to a qualitative) alteration, albeit in a long established tradition. What might be expected as a result of such a change? Well, since the fundamental concept of requiring a unanimous guilty-verdict would remain intact, we might expect an increase in convictions of roughly 1/12 or about 8%, because that would be a reasonable first-order expectation for easing the task of reaching unanimity.

Furthermore, as my cognitive-scientist "partner in crime" (so to speak) has suggested, a possible secondary effect might be to increase the difficulty of reaching unanimity due to the decrease in peer pressure from a smaller-sized jury. Perhaps a 7% overall increase in convictions might ensue. Note that this makes the secondary effect a conservative effect — it constrains the consequences of the reduction in jury size.

So if, like me, you feel that the ratio of erroneous acquittals per erroneous conviction has become excessive (i.e., too many killers are allowed to kill again), perhaps you would not be averse to a modification of the the 12-person jury. If not, you might want to consider whether or not there is an intrinsic qualitative basis for the historical choice of a 12-person jury.

Post #1,130 The Rule of 11