Question

help please

Answer 1

The test screens a blood sample for the presence of antibodies to HIV. Like most tests, this test is not
perfect. The table below shows the approximate probabilities of positive and negative EIA tests when
the blood does and does not actually contain the HIV antibodies. Long range studies have shown that
only 2% of the population actually has the HIV antibodies.
Test Result Positive Negative
Antibodies Present 0.9985 0.0015
Antibodies Not
Present
0.006 0.994
a) Explain in context all four values in the table. That is, what does each of them actually mean?
Construct a tree diagram to answer the following questions. The first two choices of the tree should be
whether or not the antibodies are present. The second choice should be the test result. (What is the
probability split for the first choice?)
b) What is the probability that a person without HIV will have a test come out positive (this is called a
false-positive)?
c) What is the probability that a person with HIV will have a test come out negative (this is called a false
negative)?
d) What is the probability that a person with HIV will have a test come out positive?

Answer 2

okay i am just trying this out for the first time

Answer 3

Glad that you're taking attempts!

Answer 4

it looks complex but i am going to try

Answer 5

positive .9985 .006 negative .0015 .994 that is the table

Answer 6

Yes, and then?

Answer 7

i think the values in the table mean that the tested people that have antibodies present was positive .9985 menaing they have hiv and im not sure what the negative means if there isnt any or used to be.

Answer 8

same with the not present.

Answer 9

positive means that the test says that they have HIV

Answer 10

so .0015 is people tested negative antibodies how is that possible?

Answer 11

.0015 is test says they don't have HIV but turns out that they do

Answer 12

ohhhh so .994 are people who thought they didnt have it but actually do?

Answer 13

no

Answer 14

or tested

Answer 15

.994 is tested that they don't have HIV and in fact they don't have HIV

Answer 16

so how would i go about finding the probability like in letter b?

Answer 17

Find out which grid the question's talkin' about

Answer 18

im really not sure

Answer 19

i thought you could take the positive and the negative to find the answer but im confused

Answer 20

well as far as i could understand :P
the table is showing the results after testing persons with HIV (the first part) and persons without HIV (the second part)
so the tests shows that from the people having HIV 0.9985 of the people give positive results and 0.0015 gives negative results. and same for the test for not present HIV.

so the tree diagram will be