Homework Help: math

Posted by jessie on Sunday, May 16, 2010 at 10:05am.

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 - drwls, Sunday, May 16, 2010 at 11:45am
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

Answer this Question

Related Questions

Statistic - Case 6.4 Maternal Serum Screening Test for Down syndrome Please ...
Statistics - One of my classmates ask this question and it wasn't answered ...
Biology- Human Karyotyping - Could someone help me find 2 disorders that are the...
Biology - Down syndrome or trisomy 21, in humans is caused by an extra copy of ...
Science - How does having William's Syndrome have a impact on peoples daily ...
Chemistry - Is cutting a tree reversible? Several things come to mind, maybe not...
Risk, Loss Prvnt, Emrgncy Plan - Assess the similarities and differences ...
MATH - tree diagra probability: tree diagram with three equal parts, what is the...
Risk, Loss Prvnt, Emrgncy Plan - Assess why we state the impact of an adverse ...
Math - David the monkey is looking down at a 33° angle from the top of a ...

For Further Reading

First Name:
School Subject:
Answer: