I have not read the entire study by Robert Weisberg, JD, PhD yet - however it does go on to say "....that report striking findings of marginal deterrence, even up to 18 lives saved per execution..." - so this is dealing with "social science" more than statistics. Quite frankly I don't buy it and I don't see how anyone could even dream up such a theory seeing how the states that do NOT have the death penalty seem to have the lowest murder rates. But, as you said, we'll probably never really know if it is a deterrent or not - although I suspect if you asked the convicted if they considered it you would probably hear"no" all the time.

There are other issues to consider as well now too - some states (such as FL) have death penalty for cases were no one has even died (such as the drug-kingpin one). These guys are making roughly 17,000% profit, and when there are numbers like that involved there isn't much you can do to stop it - but of course that's a whole other mess...ha

>Regardless of anyone's position on it, we'll probably never really know if it was or ever will be a deterrent. Even those against it show there are not enough capital punishments to do any study:
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>"A number of papers have recently appeared claiming to show that in the United States executions deter serious crime. There are many statistical problems with the data analyses reported. This article addresses the problem of 'influence,' which occurs when a very small and atypical fraction of the data dominate the statistical results. The number of executions by state and year is the key explanatory variable, and most states in most years execute no one. A very few states in particular years execute more than five individuals. Such values represent about 1 percent of the available observations. Reanalyses of the existing data are presented showing that claims of deterrence are a statistical artifact of this anomalous 1 percent."
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>http://deathpenalty.procon.org/viewanswers.asp?questionID=000983