Re: Info on The Measurements


Phil Holman wrote:
"Bob Dole" <tsdev@xxxxxxxxxxxx> wrote in message
news:1154479268.726047.243070@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Phil Holman wrote:
T/E Ratio - legal ratio 4:1 or less
13C/12C - a normal ratio -21.3 to -24.4/1000 (delta 13C/1000 range)
Typical user ratio -27.43 +/- 0.76/1000 (mean and SD).

Following on from a previous discussion on the accuracy of the
testing,
the 13C/12C ratio is very sensitive to error of measured values. This
isn't a case of categorical data (it's either synthetic or it isn't);
the determination is made from what should be very precise quantitive
data.

We know what Floyd's T/E ratio is; I've seen all the reports and it
ranges from 5:1 to 11:1 (LOL). I do hope we get a reliable report on
his
delta 13C value.

I lack the informational base to understand what you are saying above.
A ratio of two positive counts can't be negative, so I'm going to
assume that's the log of the ratio. I'm going to try to put what you
said above in different terms, so you can see where I'm likely lost.

Let's suppose there are 10,000,000,000,000 carbon 12 atoms observed
(1*10^13).

If we observed 5617 carbon 13 atoms, this would be a ratio of 5617/
10,000,000,000,000, which is a tiny number. The natural log of this
ratio would be -21.3.

If we observed 253 carbon 13 atoms, this would be a ratio of 253/
10,000,000,000,000, which is a tiny number. The natural log of this
ratio would be -24.4.

In the typical drug case, there is a ratio of -27.43 which would be 12
carbon13 atoms out of 10,000,000,000,000.

If we go down 3 standard deviations on this ratio (-27.43 +3*.76 =
-25.15), this would be 119 atoms.

Since I didn't make use of the "/1000" above I think I've
misunderstood
something. Also, this sounds like a lot of carbon atoms for a urine
sample that's mostly water, but I'm again ignorant.

A delta 13C/1000 value is used which I take as converting to a range of
975.6/1000 to 978.7/1000 for a normal 13C/12C ratio [-21.3 to -24.4/1000
(delta 13C/1000 range)]
A "user" ratio would be 972.57/1000 +/- 0.76 which means that approx
2/3rds of the subjects tested fell within the range of 971.81/1000 to
973.33/1000.


It's also not clear from your post whether the measurement error is
already factored into the normal range. In other words, is that
normal ratio based on "normal measurements given this amount of urine
tested under these conditions" -- in which case the applicable
measurement error is already factored in -- or is it the normal ratio
based on idealized information, in which case measurement error would
be an additional source of error?

Any kind of distribution will include some error in measurement but
nothing like the 20% error mentioned in a previous post. See the
"Testosterone Testing: More on False Positives" thread (7/29/06). We are
looking at a difference as small as 3/1000 to determine either a
positive or negative result which means it is very sensitive to error.


This isn't a criticism; just wondering. This isn't stuff I ever
figured I'd want/need to know about.


Phil H

Does this mean that the representative of mass spectrometer
manufacturer had it right when he pointed out that there are regularly
errors in isotope tests.

"But a more-cautious note was sounded by Dr. Davis, who is now the
technical director for Mass Spec Solutions Ltd., a Wythenshawe, U.K.,
maker of mass-spectrometry devices. "Quite regularly there are errors
in the isotope tests," he said. "It's a very difficult analytical
technique.""

The WSJ article this quote is from concluded:

"The apparent sensitivity of the testosterone test's numbers to alcohol
consumption, and the announcement of partial test results without full
disclosure by the cycling union, has created a milieu for cyclists that
is "almost Kafka-esque," Dr. Davis said. "The phrase often bandied
about is 'chemical McCarthyism'.""

http://online.wsj.com/public/article/SB115444904804023475-b3Yk05K97EtFKvdjhAVAvcCleyE_20060831.html?mod=tff_main_tff_top

.

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