From: bobb@tekig1.PEN.TEK.COM (Robert W Bales)
Newsgroups: talk.origins
Subject: Re: In case Bales has convinced you of his honesty...
Date: 17 Dec 92 20:32:00 GMT


Bill Jefferys writes:

#} me

#}I don't remember now which postings I responded to.  However, the quotes show
#}that I did not ignore the subject.  In addition, on November 4, I posted a
#}quote from "Use of Correlation Statistics with Rubidium-Strontium Systemics,
#}by Felix Chayes _Science_, vol 196, June 10, 1977, pages 1234-1235
#}
#}
#}     "It is possible, of course, that the common element bias is
#}     negligibly small, but this is a matter requiring demonstration
#}     or convincing rationalization in each specific case.  That the
#}     denominator may perhaps be serving only as a convienient scaling
#}     device provides no escape; use of an uncorrelated scaling
#}     variable whose varience is sufficiently large will impose strong
#}     positive correlation on *any* pair of variables whose negative
#}     correlation is less than perfect.  That the scaled data cluster
#}     closely about a regression line is then mearly a consequence of
#}     the choice of scaling variable and says nothing about the nature
#}     of the relation between the variables being scaled."  (page
#}     1234)

>I took the trouble to look up this article, along with the rebuttal by
>Brooks, Strobel, James and Hart that immediately follows it (p. 1235). 

>Briefly, the discussion in the quoted paragraph addresses a technical point
>in statistics whereby, when quantities X, Y, and Z are statistically
>independent, nevertheless the quantities X/Z and Y/Z (corresponding to the
>two isotope ratios in the Rb-Sr isochron method) may acquire a correlation,
>which will show up as a nonzero slope, or bias. While this is true, it is
>irrelevant to the case of Rb-Sr dating,

Then why did a standard, presumably referreed, scientific journal think the
criticism relevant enough to publish?

>since the data are highly correlated to begin with.

I thought that the theory of isochron dating was that data would be correlated
if and only if the data were the result of the age of the sample.  So the
theory goes, if a sample is contaminated or has otherwise been affected by
a process changing the isotope ratios, we will know it precisely because the
data will NOT be highly correlated.  Extraneous processes are said to produce
the same kind of data which Bill, by implication, sayes the above criticism
applies to.

We can divide the samples into two cases:

1. Samples which hsve been affected by age only, and for which the data are
   correlated.  The false, statistically induced correlation, does not apply
   to such data.  The correlation we observe in the form of the isochron
   line is real, and the isochron line indicates a real age.

2. Samples which hsve been affected by processes other than age only, and for
   which the data are uncorrelated.  In this case, statistics can induce a
   false correlation.  The correlation we observe in the form of the isochron
   line could be false, and the isochron line may indicate a false age.

Since the obseved results in the two cases are the same, we cannot tell
whether or not the original data was or was not correlated, and hence cannot
say that the statistical effect is irrelevant.  The self-checking claim for
isochrons is shown to fail.  (Just as it is shown to fail by examples of
incorrect isochon dates.)

>Brooks _et. al._ demonstrate convincingly that the ratio correlation effect
>is negligible in this case.

There is a criticism by Chayes and a response.  There is no referee quoted as
saying that the first is wrong and the second is a convincing demonstration.
Bill's claim appears to be stronger than that of the authors of the rebuttal,
for they say only:

     "Thus, in replying to Chayes, we must defend not only our recent Rb-Sr
      mantle isochron proposal, but also the Rb-Sr isochron concept in
      general.  We believe that we can successfully do both." (page 1235)

And if the effect is negligible in this case, as the rebuttal claims,
*something* is going on.  An example which shows dates measuring too old by
over 3 billion years (and which are said by others than Chayes -- Carter,
Evensen, Hamilton, and O'Nions, "Neodymium and Strontium Isotope Evidence for
Crustal Contamination of Continental Volcanos," _Science_, vol 202, November
17, 1978, pages 743-747 -- to have no age meaning at all) is certainly NOT an
argument for the trustworthiness of isochron dating!

>They effectively put to rest Chayes' concern that this effect may be
>significant for Rb-Sr dating.

Not necessarily.  Quoting from the rebuttal:  "The framework of the Rb-Sr
systematics is model-dependent." (page 1235)  In other words, the defense that
the model is correct is  based partially on the assumption that the model is
correct.  Note also that the rebuttal says:

     ". . . .Chayes`s criticism can also be safely ignored for most
     mantle isochrons.  However in the interpretation of slopes no
     normative statistical statement should be accepted, but each
     plot should be examined in the light of all available infor-
     mation."  (page 1235)

Although this is listed for mantle isochrons, I think it should apply to all.
So where is the data for the 5 isochons whose agreement is said to prove the
earth is billions of years old?

(Incidently, what is the reference for those 5 isochron dates?  If it has been 
listed here at all, it was several years ago. I do not mean to imply that it
doesn't exist, but would just like to know what it is.)

>Did Bob actually read Chayes' article,

Yes.

>or is he quoting from some Creationist tract? If the latter, he is
>irresponsible;

Bill read Chayes's article. and did not correct my quotes, so they must have
been accurate.  I also quoted, in my original articles, from the rebuttal.
I took these quotes directly from the articles.  The point is, however, that
since they were accurate and mentioned both sides of the issue, they were
not irresponsible, whatever their source.

>if the former, how can he not have seen the rebuttal,

I saw the rebuttal, as indicated by my quoting from it in my original article.

>and if he did see the rebuttal, why is he using this article at all?

For several years now, I have been told in this group that no process other
than aging would produce a straight-line isochron and have been challenged to
provide a definite process which could do so.  I reference the article by
Chayes because it does so.  The rebuttal to the article doesn't change this.
Even though Brooks, et. al. and also Bill don't think the process applies to
the examples of isochron dating, they agree that it could impose the
appearance of correlation on uncorrelated data.  I've discussed above why I
think this is of practical importance.

>Now, for all to see, I will post, AGAIN, the article that Bales has been
>ignoring for nearly two years. I see no  reason to respond to Bales
>ruminations until he has the courtesy to answer these questions.

During one of my absences some time ago, I completed a response, but did not
post it at that time because I was too involved in discussing other matters.
I will post it -- updated with the latest information on isocrons -- in a
series of articles following this one.

   Bob Bales
   Tektronix, Inc.

I help Tektronix make their instruments. They don't help me make my opinions.