Tag Archives: maths

The Mathematics of NT-plus Screening

Update: regular commenter Mark L has helpfully identified they reason behind the apparent anomaly in the statistics that motivated me to write this post. I had misinterpreted one of the statistics. While this takes the mystery out of the numbers, it does highlight how tricky it can be to get to grips with the statistics of medical tests. I have edited this post to correct that misinterpretation. I decided not to use a the strikethough editing approach popular among bloggers as the content can be confusing enough already!

Despite the fact that more banks have been failing (Bradford & Bingley, Wachovia, Hypo Real Estate, Fortis,…), in this post I will continue to stay away from the subject of the financial markets and will instead look at some mathematics, trying not to lose too many readers in the process.

Recently I was contemplating results from an “NT-plus” test, which combines ultrasound measurements of the nuchal translucency with maternal blood-tests to provide a screening test for various chromosomal abnormalities, particularly Down Syndrome. Tests of this type abound with statistics and the mathematician in me could not resist crunching the numbers a little to get a better understanding of the test.

Continue reading

The Garnaut Report and “Tit-for-Tat”

For those outside Australia, the Garnaut Climate Change Review is our equivalent of the Stern Review and last week a draft report was released. In this report, a nation’s decision as to how to act in the face of climate change is compared to the prisoner’s dilemma:

Effective international action is necessary if the risks of dangerous climate change are to be held to acceptable levels, but deeply problematic. International cooperation is essential for a solution to a global problem. However, such a solution requires the resolution of a genuine prisoners’ dilemma. Each country benefits from a national point of view if it does less of the mitigation itself, and others do more. If all countries act on this basis, without forethought and cooperation, there will be no resolution of the dilemma.

Continue reading