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drug/alcohol testing policy: effective?



 
 
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  #1  
Old December 17th 04, 05:14 PM
Chip Jones
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"Michael" wrote in message
ups.com...
Chip Jones wrote:
The bottom line is that the THREAT of being popped positive on a

random drug
test seriously deters drug use. In the field of professional

aviation, that
is a good thing.


No, the bottom line is that the rate of use in aviation is so low (as
indicated by the results) that most if not all of the positives are
false positives. If it's worth doing, it's worth doing right - and
since nobody seems willing to spend the money to do it right
(eliminating the false positives) I have to assume it's not worth
doing.


Michael, just wondering, what makes you think that nobody seems willing to
spend the money to do drug testing the "right" way?

The method madated by the FAA ala a DOT 49 CFR Part 40 random urine drug
test is called a GC/MS drug test. GC/MS drug testing has virtually *no*
false positives. No test can be 100% accurate, but the GC/MS test combined
with the MRO process is pretty dang accurate.

You can read all about it he http://www.aviationmedicine.com/drugtest.htm

Chip, ZTL


  #2  
Old December 18th 04, 07:05 PM
Gary Drescher
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"Chip Jones" wrote in message
k.net...
The method madated by the FAA ala a DOT 49 CFR Part 40 random urine drug
test is called a GC/MS drug test. GC/MS drug testing has virtually *no*
false positives...

You can read all about it he
http://www.aviationmedicine.com/drugtest.htm


Nothing at that web page states that the test has a low false-positive rate.

The false-positive rate isn't even inherent in a test itself. Specificity is
an inherent property of a test--but even an excellent test with very high
specificity can still have an arbitrarily high false-positive rate if
applied to a population in which positive examples are sufficiently rare.
(The web page says nothing about the test's specificity either, by the way.)

Do you have support elsewhere for your "virtually no false positives" claim?

--Gary


  #3  
Old December 19th 04, 11:25 AM
Chip Jones
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Posts: n/a
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"Gary Drescher" wrote in message
...
"Chip Jones" wrote in message
k.net...
The method madated by the FAA ala a DOT 49 CFR Part 40 random urine

drug
test is called a GC/MS drug test. GC/MS drug testing has virtually *no*
false positives...

You can read all about it he
http://www.aviationmedicine.com/drugtest.htm


Nothing at that web page states that the test has a low false-positive

rate.

The false-positive rate isn't even inherent in a test itself. Specificity

is
an inherent property of a test--but even an excellent test with very high
specificity can still have an arbitrarily high false-positive rate if
applied to a population in which positive examples are sufficiently rare.
(The web page says nothing about the test's specificity either, by the

way.)

This is an issue that I can neither defend or attack, because I can't
quantify in my mind what an "arbitrarily high" false positive rate would be
in a test group like commercial aviators, where positive examples are, I
agree, very rare. To me, it is sufficient that GC/MS testing is very
accurate at detection and errs on the side of the person being tested (see
the false positive rate in the link below from a study from NIDA comparing
self reporting to GC/MS testing, which mentions the false-positive rate of
the GC/MS test across the spectrum).


Do you have support elsewhere for your "virtually no false positives"

claim?



Here are a few links:

Here's one from NIDA, where the false positive rate in GC/MS drug testing
for THC was 0.3 to 3.1%, and this was before any MRO action as per the DOT
CFR.

http://www.drugabuse.gov/pdf/monogra...6_Harrison.pdf

Here are some on the accuracy of GC/MS testing from some "how to beat the
test" camps. The first one says:

"Gas Chromatography Mass Spectrometry (GC-MS)
GC/MS is the most precise method of testing, it is so precise that
guidelines set by NIDA (National Institute on Drug Abuse) require positive
immunoassay (emit ), and gas chromatography tests be confirmed by a GC-MS
test. Only the Federal Government is required to follow these guidelines and
unfortunately most companies due not follow these guidelines. In other words
should you test positive falsely the GC-MS will confirm that you are not a
drug user, however the odds your tester confirms positive tests with GC-MS
are miniscule (why? It is expensive)."

http://www.streetdrugtruth.com/testing/testtypes.php4

And some more from pro-drug, anti-test groups on GC/MS testing accuracy:

http://cocaine.org/drugtestfaq/index.html

http://www.neonjoint.com/passing_a_d..._accuracy.html

http://www.ushealthtests.com/dtbasics.htm

http://www.onlinepot.org/misc/****tests.htm


Chip, ZTL





  #4  
Old December 19th 04, 02:07 PM
Gary Drescher
external usenet poster
 
Posts: n/a
Default

"Chip Jones" wrote in message
ink.net...

"Gary Drescher" wrote in message
...
"Chip Jones" wrote in message
k.net...
The method madated by the FAA ala a DOT 49 CFR Part 40 random urine

drug
test is called a GC/MS drug test. GC/MS drug testing has virtually
*no*
false positives...

You can read all about it he
http://www.aviationmedicine.com/drugtest.htm


Nothing at that web page states that the test has a low false-positive

rate.

The false-positive rate isn't even inherent in a test itself. Specificity

is
an inherent property of a test--but even an excellent test with very high
specificity can still have an arbitrarily high false-positive rate if
applied to a population in which positive examples are sufficiently rare.
(The web page says nothing about the test's specificity either, by the

way.)

This is an issue that I can neither defend or attack, because I can't
quantify in my mind what an "arbitrarily high" false positive rate would
be
in a test group like commercial aviators, where positive examples are, I
agree, very rare.


Well, here are some illustrative numbers to help envision how an accurate
test could produce an arbitrarily high false-positive rate. Suppose the test
has a specificity of 99% and also a sensitivity of 99%. Specificity refers
to the proportion of negative examples that correctly test negative;
sensitivity is the proportion of positive examples that correctly test
positive.

Now, suppose you apply this very accurate test to a population of one
million, among whom there are 1,000 positive examples. Among the 1,000
positive examples, about 990 will test positive, and about 10 will test
negative. Among the 999,000 negative examples, about 989,010 will test
negative, and about 9,900 will test positive.

Thus, among the 10,890 who test positive, 990 are actually positive
examples, and 9,900 are actually negative examples. Thus, the false-positive
rate (the proportion of the positive test results that are false) is about
90.9%. Despite the use of an accurate test (99% sensitivity and
specificity), more than 90% of those who test positive will actually be
negative.

Here's one from NIDA, where the false positive rate in GC/MS drug testing
for THC was 0.3 to 3.1%, and this was before any MRO action as per the
DOT
CFR.


Again, the false-positive rate *is not a function of just the accuracy of
the test*. A highly accurate test (high sensitivity and specificity) might
have an arbitrarily high or arbitrarily low false-positive rate, depending
on the proportion of actual positive and negative examples in the tested
population. Thus, a test's false-positive rate applied to one population
tells you nothing about the same test's false-positive rate applied to a
different population.

--Gary


  #5  
Old January 28th 05, 06:19 AM
Chip Jones
external usenet poster
 
Posts: n/a
Default


"Gary Drescher" wrote in message
...
"Chip Jones" wrote in message
ink.net...

"Gary Drescher" wrote in message
...
"Chip Jones" wrote in message
k.net...
The method madated by the FAA ala a DOT 49 CFR Part 40 random urine

drug
test is called a GC/MS drug test. GC/MS drug testing has virtually
*no*
false positives...

You can read all about it he
http://www.aviationmedicine.com/drugtest.htm

Nothing at that web page states that the test has a low false-positive

rate.

The false-positive rate isn't even inherent in a test itself.

Specificity
is
an inherent property of a test--but even an excellent test with very

high
specificity can still have an arbitrarily high false-positive rate if
applied to a population in which positive examples are sufficiently

rare.
(The web page says nothing about the test's specificity either, by the

way.)

This is an issue that I can neither defend or attack, because I can't
quantify in my mind what an "arbitrarily high" false positive rate would
be
in a test group like commercial aviators, where positive examples are, I
agree, very rare.


Well, here are some illustrative numbers to help envision how an accurate
test could produce an arbitrarily high false-positive rate. Suppose the

test
has a specificity of 99% and also a sensitivity of 99%. Specificity refers
to the proportion of negative examples that correctly test negative;
sensitivity is the proportion of positive examples that correctly test
positive.

Now, suppose you apply this very accurate test to a population of one
million, among whom there are 1,000 positive examples. Among the 1,000
positive examples, about 990 will test positive, and about 10 will test
negative. Among the 999,000 negative examples, about 989,010 will test
negative, and about 9,900 will test positive.

Thus, among the 10,890 who test positive, 990 are actually positive
examples, and 9,900 are actually negative examples. Thus, the

false-positive
rate (the proportion of the positive test results that are false) is about
90.9%. Despite the use of an accurate test (99% sensitivity and
specificity), more than 90% of those who test positive will actually be
negative.

Here's one from NIDA, where the false positive rate in GC/MS drug

testing
for THC was 0.3 to 3.1%, and this was before any MRO action as per the
DOT
CFR.


Again, the false-positive rate *is not a function of just the accuracy of
the test*. A highly accurate test (high sensitivity and specificity) might
have an arbitrarily high or arbitrarily low false-positive rate, depending
on the proportion of actual positive and negative examples in the tested
population. Thus, a test's false-positive rate applied to one population
tells you nothing about the same test's false-positive rate applied to a
different population.


Thanks Gary, that's clearer to me now.

Chip, ZTL


 




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