On Fri, 16 Mar 2001, Rich Ulrich wrote:
> Elliot,
>
> It appears to me that Arnold Barnett is guilty
> of a serious misuse of statistical argument.
>
> I don't think readers are apt to be misled by the media
> reports; there is a very LOW rate of capital punishment
> in the US, so the likelihoods are (indeed) essentially
> the same as Odds Ratios.
This is not a RAW difference which, I'm sure you agree, is not relevant to
anything. It's the same problem as comparing University salaries between
men and women. Men are much more likely to be full professors for
historical reasons (40 years ago few women got PhDs). Faculty rank is
relevant to salary as are a host of other variables and must be taken into
account. In the death penalty situation the nature of the homicide must
be taken into account (you don't get the death penalty for running over
someone with a car. The odds ratio quoted is for a model that includes a
host of relevant variables IN ADDITION to race. I don't think that there
is ANY good statistical evidence of racial discrimination in the death
penalty, but that's another issue. The point here is that there are many
situations( such as the one illustrated) for which a death penalty has a
high probablility which is VERY different from the odds ratio.
>
> When I saw mention of these data a few years ago, my first tendency
> was to doubt the "what-if." P[death sentence] = 0.99? not
> generally.... Rates of executions are low, as I said earlier.
not for serial killers or for the type of homicides which lead to the
death penalty
>
> - Now, the author is asserting that 1% versus 4% is far different
> from 99% versus 96%. Statisticians should be leery of that.
>
NO; I think he is asserting that 20% vs 80% is far different
> - the judges and journalists missed the word; they missed the math
> that would have made the word important; so they ended up with the
> right conclusion.
>
I don't think they ended up with the right conclusion at all. Heinous
murderers tend to get the death penalty whether they murder blacks or
whites.
The point of the article is that the Supreme Court apparently understood
the odd ratio to be a probability ratio. The US district court did not
make this mistake and issued a devastating critique of the Baldus Study
which used linear regression instead of logistic regression, amongh other
things. It was VERY inadequate in dealing with nature of the crime which
is the most important consideration in the death penalty.
Interestingly most murder are within race; blacks murder blacks and
whites murder whites. Baldus finds no discrimination based on race of the
murderer, only of the victim.
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