Help ! Propability?? HELP?

Question

Diagnostic tests of medical conditions have several results. The test result can be positive of negative, whether or not the patient has the condition (+ indicates the patient tested positive for the condition). Consider a random sample of 200 patients, some of whom have a medical condition and some of whom do not.

Results of a new diagnostic test for the condition are shown. For a person selected at random compute the following.

Condition Present Cond Absent Row Total

Test Results + 110 20 130

Test Results - 20 50 70

Column Total 130 70 200

a. P(+, given condition present)

b. P(-, given condition present)

c. P(-, given condition absent)

d. P(+, given condition absent)

e. P(condition present and +)

f. P(condition present and -)

1 day ago - 2 days left to answer.

Answer 1

Despite the medical context, this is really a stats question.  You might want to try your luck in Mathematics or in Homework Help.

http://answers.yahoo.com/dir/;_ylt=AjMRx...

http://answers.yahoo.com/dir/;_ylt=Ap6YD...

Anyway, (a) to (d) are what's known as conditional probabilities.  For example, for (a), since you are "given" that the condition is present, you only have to look at the first column ("Condition Present"), which has a total of 130.  In this column, the probability of "+" is 110/130 = 0.846 = 84.6%.

Following the same logic, you should be able to figure out (b), (c) and (d) on your own.  (We are here to help, not to do your homework for you.)

For (e) and (f), you simply divide the cell which fits the criteria by the total of 200.

Good luck.