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This 2011 article in the BMJ (British Medical Journal) by Professor RWK Chiu et al uses Z-tests on a single sample of data from each of 753 pregnant women to test the proportion of DNA molecules in the mother's plasma (blood) that originated from chromosome 21.
Our normal cell DNA consists of 23 pairs of chromosomes, one each from each parent. In people with birth defects, there are more than 2 (typically 3 - a trisomy) of some chromosomes. For example, people with Down Syndrome have 3 copies of chromosome 21 instead of 2.
Screening or detection of these abnormalities (which tend to cause health problems such as shorter life-span and social problems due to non-acceptance in society) before birth (prenatal screening) has in the past invovled testing the amniotic fluid by extracting it with a needle from the amniotic sac. This may cause stress to the baby/phoetus and potentially cause miscarriage, and is hence regarded as invasive.
This sampling of the blood plasma of the mother, where DNA from the phoetus is present (as it has crossed the placenta into the mother's bloodstream), is much safer and may provide the information needed.
The outcome they measure is the proportion of DNA originating from chromosome 21. They convert the measure into a Z-score (subtract the expected mean and divide by the variance) and test that for each woman. They conclude that the accuracy of their procedure is such that 98% of invasive diagnostic procedures (namely, testing the amniotic fluid) could be avoided.
This question is a big ask, because peer-reviewed articles of importance (easily found on the internet) are about cutting-edge science. The developments using this method will tend to be seen in applied science journals. This journal is a medical journal and the articles tend to be full of a lot of medical jargon and are about complicated medical advances. Hence, you might find this article difficult to read and understand! That is why I've tried to explain above.
Answer: Article using Z-tests on single samples
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