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#1
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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
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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
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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
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"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
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![]() "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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