# math

posted by .

how do you form the probability tree for this??

The commonly used test to assess Down's syndrome risk in the unborn foetus is the 'triple test', which combines maternal age with other markers of foetal and maternal health from a single blood test. The test has a 65% detection rate, and a 5% false positive rate. Incidence of Down's syndrome in births from 35 yr old mothers is 1 in 250. The triple test from one 35 yr old mother returns a positive result. What is the probability that her foetus has Down's syndrome?

• math -

Out of a random sample of 35 year old mothers:

Probability of false positive = (249/250)*0.05 = 0.0498
Probability of correct positive = (1/250)*0.65 = 0.0026
Probability of false negative (undetected Down's) = (1/250)*0.35 = 0.0014
Probability of correct negative = (249/250)*0.95 = 0.9462

For the woman in question, she is either a false positive or a correct positive.

Probability of Down's = (.0026)/(.0026+.0498) = 0.04962
That equals a probability of 1 in 20.2

## Similar Questions

1. ### Bio Science

The majority of nondisjunction events leading to Down syndrome are maternal in origin. Based on the duration of meiosis in females, speculate on the possible reasons for females contributing aneuploid gametes more frequently than males.
2. ### Biology- Human Karyotyping

Could someone help me find 2 disorders that are the result of non-disjunction. I already have down syndrome, klinefelter syndrome, Turners Syndrome, Super Males, Triple X syndrome, Edward's syndrome and Patau's syndrome. Thanks in …
3. ### math

Samantha has an average of 92% on tree math test. If one of her grades was 84% and the other is 93%, what was the grade of her third test?
4. ### Statistic

Case 6.4 Maternal Serum Screening Test for Down syndrome Please keep in mind that I do not have a Math back ground so this is brand new to me and like a foreign language that I have never seen nor heard spoken before. Thank you for …
5. ### Statistics

One of my classmates ask this question and it wasn't answered so now I am asking it and of course we are all struggling with no strong Math background Case 6.4 Maternal Serum Screening Test for Down syndrome Please keep in mind that …
6. ### Biology

A student claims the probability a human sperm will receive all chromatids of maternal origin is 50 %. Explain why she is wrong.
7. ### Biology

A student claims the probability a human sperm will receive all chromatids of maternal origin is 50 %. Explain why she is wrong.
8. ### Physiology

When maternal oxygen is transferred to the fetus and fetal CO2 is passed back, how does this affect the maternal dissociation curve?
9. ### Health (Ms. Sue)

Explain the relationship between the key terms in each of the following pairs. a. HIV-antibody test and HIV positive b. HIV and universal precautions A: a. HIV-antibody test and HIV positive correspond with each other as HIV positive, …
10. ### Writing

They emphasized the importance of good maternal and child health care, including the administering of vaccines.

More Similar Questions