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Sampling Bias

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Anyone teaching a course in study methodology need a pristine example of sampling bias?  Just look at the op-ed by former correctional officer Marshall Thompson, noted in the prior post on the weekend Prop 34 op-eds.

"I helped put four men to death at San Quentin. I've known hundreds of others on death row. Not a single one of them thought he'd get caught."

Well, of course not.  By definition, the ones on death row are the ones who were not deterred.  The potential killers who were deterred did not commit the crimes and are not on death row.  They are not in prison at all, unless for some other crime.

Isn't that perfectly obvious?  Will anyone fall for such a patently invalid argument?  Sadly, yes.  Logic isn't taught much in schools any more.

Nobody on our side, that I know of, has ever claimed that deterrence is 100% effective.  (Such a claim would be preposterous on its face.)  For anecdotal evidence that the deterrent effect of the death penalty does save lives, see the video clip of Robert Blecker's testimony in the London mock trial event, linked in this post.  For econometric studies, see the deterrence page of our web site.

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Where the DP is available to accomplices and co-conspirators, the existence of the DP likely influences the criminal group to police each other. No one wants to die because one of his buddies decided to get stupid.

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