c**i
发帖数: 6973 | 1 Pam Belluck, Is It Boy Or Girl? A Test At 7 Weeks; Simple DNA analysis with
high accuracy. New York Times, Aug 10, 2011.
http://www.nytimes.com/2011/08/10/health
/10birth.html?_r=1&scp=1&sq=dna%20fetus&st=cse
Excerpt in the window of print: A fast, noninvasive measure of fetal DNA in
the mother's blood
My comment:
(a) The report is based on
Stephanie A. Devaney SA et al, Noninvasive Fetal Sex Determination Using
Cell-Free Fetal DNA; A systematic review and meta-analysis. Journal of
American Medical Association (JAMA), 306: 627-636 (2011).
http://jama.ama-assn.org/content/306/6/627.abstract?
sid=e1f99075-32bb-4f85-8a45-896302706c9e
(i) This is a review article, which, through statistics, reviews studies by
others instead of conducting its own original scientific study.
* Why scientists have little confidence in Chinese medicine is because few
research is done on it and because it has no objective, scientific tests.
* The following is about definitions of parametrics of an accurate
diagnostic test. These definitions may be difficult for layperson to
comprehend. If so, jump to the last item, (b).
(ii) Please see definitions in
sensitivity and specificity
http://en.wikipedia.org/wiki/Sensitivity_and_specificity
The studies under scrutiny all conduct tests on "Y chromosome sequence." So
sensitivity means percentage of a male (who has Y) that is correctly called,
and specificity, percentage of a female (who does not have Y) that is
correctly identified.
(iii) The "95% confidence interval" measn within TWO standard deviations 標
準差 on both tails.
http://en.wikipedia.org/wiki/Standard_deviation
(iv) This is the first research paper that proposed the use of "diagnostic
odds ratio" (DOR).
Glas AS et al, The Diagnostic Odds Ratio: a Single Indicator of Test
Performance. Journal of Clinical Epidemiology 56: 1129–1135 (2003).
http://vanguardia.udea.edu.co/cursos/Memorias%20precongreso
%20aede/2.4.%20Estudios%20de%20pruebas%20diagn%F3sticas
/Diagnostic%20Odds%20Ratio.pdf
A "single" indicator, because it combines sensitivity and specificity
together into one.
* Formula (1) in the paper present the equation:
DOR = "TP/FN" devided by "FP/TN" = "sens/(1-sens)" devided by "(1-spec)/spec"
, where TP stands for true positive;
FN, false negative;
FP, false positive;
TN, true negative;
sens, sensitivity; and
spec, specificity.
* The paper, immediately following the formula, stated, "The value of a DOR
ranges from 0 to infinity, with higher values indicating better
discriminatory test performance."
(v) For Area Under Curve (AUC), see
The Area Under an ROC Curve. Division of General Internal Medicine (GIM),
University of Nebraska Medical Center (UNMC), undated.
http://gim.unmc.edu/dxtests/roc3.htm
("An area of 1 represents a perfect test; an area of .5 represents a
worthless test")
* You see, the figures in this web page has 0-1 in x axis and the same in Y
axis, making the total area 1.
* Please click the "Previous Section" twice to understand how the figure is
plotted.
(b) A handful of years ago, scientists learned that fetal cells flow in a
mother's blood, even years after the pregnancy--similar to cancer cells
flowing in a patient's blood. Tests were designed to detect either. There
were technical difficulties, as measured by parameters mentioned above. Now
the JAMA review asserts that using the fetal DNA to assign sex is good
enough. Like ultrasound, there is always false positive and false negative. | j*****g
发帖数: 7513 | | c**i
发帖数: 6973 | 3 But remeber the New York Times report says that federal government has not
certified laboratories in US to do the tests. I do not know what the
sentence means, about accuracy, legal consequence for the laboratories that
do it, etc.
【在 j*****g 的大作中提到】
: 刚刚在收音机里听到这条消息
|
|
