My view is that conclusive evidence of whether the deterrent effect is real or not remains lacking. While this state-by-state comparison is certainly better than country-by-country, it's still not unequivocable. For example, there are "death penalty states" that haven't actually executed anyone in decades, so it's unclear how they should be accounted when it comes to assessing deterrence. But I think that's all side-show - even if it were clearly shown to work, it still wouldn't justify the numbers of wrongly-executed people that we already know about. So I think it's a tactical mistake to get sucked into a technical argument on this subject - you won't end up with a clear outcome, even after expending lots of space and energy debating tons of details, and in the meantime the larger point will get lost. It's an interesting question, but I'm not sure the rate is that much lower. Looking at the variations across states, it's not clear to me that the difference is even statistically significant. Also, I'd be much more interested in seeing the median murder rates - the averages are going to be thrown around by some of the outlier states. For example, if Louisiana were to abolish the death penalty tomorrow, it's possible that would result in the murder rate for non-death-penalty states being higher than that for death-penalty states. Again, notice that this subject is a real can of worms, which is why I council avoiding it. Upshot is that even if we think that deterrence works, the death penalty is still a net loser. Yeah, but there are lots of social policies that don't make sense from a purely financial standpoint. It's not a very useful perspective for social policies. I think you can get that conclusion just as forcefully without worrying about counting money. Just ask people exactly how many innocent people a year they're comfortable executing in order to get whatever benefits they believe accrue from the death penalty. Dollars to donuts, it will be far less than the number we have been executing. I say this because I used to go back and forth on the death penalty question, and always get bogged down in all these diversions whenever I'd try to reason through it. Then I encountered an argument that focussed almost exclusively on the issue of exeutions of innocent people. It was an eye-opener to realize that I could dispense with all of the sticky questions and reach a satisfactory, clear-cut answer. Perfectionism makes for a nice slogan, but note that that same argument there applies to any kind of criminal penalties. At some point, we simply have to accept a certain cost in terms of punishments of innocent people. But the upshot is that, without getting into detailed considerations of irreversibility and gradations of severity, you'll find that if you ask people exactly how many innocents it's okay to execute, they will almost always answer a number that is far below the one we already exhibit. Point is that you can win the death penalty argument simply by focussing on advertizing exactly how many innocents are being executed - even people who greatly disagree with you on the various finer points of all the other questions will agree that it's way too high. There, now you're talking. You should be hammering this point above all the others. Essentially nobody is going to argue that it's acceptable to execute multiple innocent people every single year. Nah, that's a tragedy, but it's still not murder. It isn't really possible, technically, for a legal action to be "murder." That's for sure. At this point, if I were you, I'd settle for insisting that the burden is on advocates of the death penalty to conclusively prove that it has deterrent value. The idea that we are paying the real costs of executing innocent people, etc., without the question of whether there is any benefit at all being settled, is unacceptable.