Newsgroups: alt.activism
From: mfriedma@uucp (Michael Friedman)
Subject: Harel gets a defender (was Re: Yet another pathetic Friedman post
Organization: Oracle Corporation
Date: Fri, 2 Oct 1992 16:30:47 GMT
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In article <1992Oct1.114642.9155@vax.oxford.ac.uk> halpin@vax.oxford.ac.uk writes:
>Michael Friedman (mfriedma@uucp) quoting Harel Barzilai:

>>>        [That would make 15.5% of people in poverty Black -- Blacks 
>>>        are 12% of the population; hence poverty for Blacks is about 
>>>        30% higher than the (already abysmal) national average. 
>>>        --Harel] 

>> Actually, that would make you a mathematical illiterate.

>> If these numbers were true the poverty level for blacks would be .033%
>> compared to a national average of .025%.  The poverty rate for blacks
>> would be .008% higher than the national average.

>> You are taking a percent of a percent, something that is
>> not meaningful in this context.

>Think before you post, Mr. Friedman. It is you who is having the
>problems with statistical literacy. 

>Let's accept Harel's figures of 15.5% and 12%. 

Why should we?  After all, he apparently got them freom the same
source that says that the national povery rate is .25%.

>If we compare the
>chance of being poor for two random individuals drawn from the
>population, one black, and one race-unspecified, we find precisely
>that the black person's chance of being in the poor population is
>higher than that of the average person by a factor of 15.5/12 or
>approximately 1.292. 

Correct, but that's not what Harel said.

>In other words, if you are black, your chance of being poor is 30%
>higher than average. What's ``not meaningful'' about this?

Nothing.  Your statement is meaningful.  It is not the same as
Harel's, however.

>Your figure of .008% has a somewhat less useful interpretation. It
>represents this same relationship in terms of the ``extra'' numbers
>of poor black people (over what there would be if the black poverty
>rate equalled the average) as a proportion of the total black
>population, and is therefore dependent on the absolute level of
>poverty -- which, as you pointed out yourself, is ridiculously
>underestimated (presumably a typo) in Harel's original post. 

A pair of typos if anything.

Also, I think the .008% is a much more useful figure.

After all, this isn't like the death penalty where we are focusing in
on the particular people involve.  We're using this stat as a way of
getting a view of the entire population.  In that case, the .008%
number tells us that the poverty level shows no real difference
between the two groups, and that's right - after all, it includes so
few people that it isn't significant.

>There is nothing invalid in taking a percentage of a percentage, or
>a proportion of a proportion. 

There's plenty.  As I said above, it is sometimes meaningful, but not
in this case.
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