A test to determine whether a certain antibody is present is 99.7​% effective. T

Tolnaio

Tolnaio

Answered question

2021-09-25

A test to determine whether a certain antibody is present is 99.7​% effective. This means that the test will accurately come back negative if the antibody is not present​ (in the test​ subject) 99.7​% of the time. The probability of a test coming back positive when the antibody is not present​ (a false​ positive) is 0.003.
Suppose the test is given to seven randomly selected people who do not have the antibody.
What is the probability that the test comes back negative for all seven ​people? and what is the probability that the test comes back positive for at least one of the seven ​people?

Answer & Explanation

wornoutwomanC

wornoutwomanC

Skilled2021-09-26Added 81 answers

Step 1
Given,
The probability that the test shows negative result if the antibody is not present is p1=0.997
And the probability that the test shows positive result if the antibody is not present is p2=0.003
The test is given to n=7 randomly selected people who do not have the antibody.
Let X denote the event that the number of test turning out negative and Y denote the event that the number of event turns out positive.
Then XBom(n=7,p1) and XBom(n=7,p2)
Therefore using binomial probability the required probability that the test comes back negative for all seven randomly selected people who do not have the antibody is obtained as
P(X=7)=7C7×p17×p20
=1×(0.997)7×1
=0.9792
Step 2
Again by using binomial probability, the required probability that the test comes back positive for at least one of the seven ​randomly selected people who do not have the antibody is obtained as
P(Y1)=1P(Y<1)
=1P(Y=0)
=1[{7}C0×p20×p17]
=1[1×1×0.9977]
=109792
=0.0208

nick1337

nick1337

Expert2023-06-17Added 777 answers

Step 1. Probability of the test coming back negative for one person:
The probability of the test coming back negative for one person who does not have the antibody is 99.7%, or 0.997. Therefore, the probability of the test coming back negative for all seven people is:
P(Negative for all 7 people)=0.9977
Step 2. Probability of the test coming back positive for at least one person:
To find this probability, we can calculate the complement of the event ''the test comes back negative for all seven people.'' In other words, we want to find the probability that at least one person tests positive.
P(Positive for at least one person)=1P(Negative for all 7 people)
Let's substitute the values into the formulas:
P(Negative for all 7 people)=0.9977
P(Positive for at least one person)=10.9977
Calculating the probabilities:
P(Negative for all 7 people)0.991
P(Positive for at least one person)10.9910.009
Therefore, the probability that the test comes back negative for all seven people is approximately 0.991, and the probability that the test comes back positive for at least one of the seven people is approximately 0.009.
Vasquez

Vasquez

Expert2023-06-17Added 669 answers

The probability of the test coming back negative for a single person who does not have the antibody is given as 99.7% or 0.997. Therefore, the probability of the test coming back negative for all seven people is calculated by multiplying the probabilities together, since the events are independent:
P(N for all 7 people)=P(N1N2N3N4N5N6N7)=P(N1)·P(N2)·P(N3)·P(N4)·P(N5)·P(N6)·P(N7)=0.99770.99004493.
The probability of the test coming back positive for at least one of the seven people is the complement of the event ''N for all 7 people.'' In other words, it's the probability that at least one person tests positive. We can calculate this by subtracting the probability of all negative results from 1:
P(P for at least one of the 7 people)=1P(N for all 7 people)=10.990044930.00995507.
Therefore, the probability that the test comes back negative for all seven people is approximately 0.990,044,93, and the probability that the test comes back positive for at least one of the seven people is approximately 0.009,955,07.
Don Sumner

Don Sumner

Skilled2023-06-17Added 184 answers

Result: 0.009951.
Solution:
The probability that the test comes back negative for one person who does not have the antibody is 0.997, given in the problem. Since the results for each person are independent, the probability that the test comes back negative for all seven people is:
P(N for all 7 people)=P(N1N2N3N4N5N6N7)
Since the events are independent, we can multiply the probabilities:
P(N for all 7 people)=P(N1)·P(N2)·P(N3)·P(N4)·P(N5)·P(N6)·P(N7)
Substituting the given probability of a negative test result:
P(N for all 7 people)=0.9977
Now let's calculate the probability that the test comes back positive for at least one of the seven people. This is equivalent to finding the complement of the event that the test comes back negative for all seven people. Therefore:
P(P for at least one person)=1P(N for all 7 people)
Substituting the value we obtained earlier:
P(P for at least one person)=10.9977
Calculating the values:
P(N for all 7 people)0.990049
P(P for at least one person)10.9900490.009951
So, the probability that the test comes back negative for all seven people is approximately 0.990049, and the probability that the test comes back positive for at least one of the seven people is approximately 0.009951.

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