From a capital punishment argument that Lawrence Solum quotes:

Recent evidence suggests that capital punishment may have a significant deterrent effect, preventing as many eighteen or more murders for each execution. This evidence greatly unsettles moral objections to the death penalty, because it suggests that a refusal to impose that penalty condemns numerous innocent people to death. Capital punishment thus presents a life-life tradeoff, and a serious commitment to the sanctity of human life may well compel, rather than forbid, that form of punishment...The widespread failure to appreciate the life-life tradeoffs involved in capital punishment may depend on cognitive processes that fail to treat "statistical lives" with the seriousness that they deserve.

You know you're getting desperate when you start relying on negative statistical research to justify your claims. Unlike positive statistics -- such as the mean age of homicide victims -- negative statistics can never yield empirical certainty. They begin with a hypothetical premise and yield purely speculative results.

Yet when it comes to state-sanctioned executions, the finality of death demands moral certainty on the part of the state. As a result, if the state relies on a philosophical argument to produce that certainty, then the argument in question must be logically consistent; and if it relies on an empirical argument, then a) the statistical evidence offered must be positive, and b) the methodology used cannot have an innate margin for error.

When it comes to those latter qualifications, a life-life argument using negative statistics plainly doesn't cut it.