Another hard Biostat question

[stronghold]

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Scientists want to investigate a new test for prostate cancer and compare it with the gold standard test. In a sample of 100 persons, 70 had a positive result using the gold standard test. While the new test resulted in 50 positive results. Which of the following sentence is correct if the 50 positive results were true positive?

1) The new test is high sensitive
2) FP in the new test is more than the gold standard test
3) The nest is high specific
4) The sensitivity of the test is 50%

 

[Leon22]

Scientists want to investigate a new test for prostate cancer and compare it with the gold standard test. In a sample of 100 persons, 70 had a positive result using the gold standard test. While the new test resulted in 50 positive results. Which of the following sentence is correct if the 50 positive results were true positive?

1) The new test is high sensitive
2) FP in the new test is more than the gold standard test
3) The nest is high specific
4) The sensitivity of the test is 50%

because the other options are not likely
what 's the correct answer?

 

[ButterfingerBBs]

+ -
+ 50 0 50
- 20 30 50
70 30 100

TP=50, FP=0, FN=20, TN=30
Sen: 50/70=71%
Spec: 30/30=100%

Answer 3: Test is highly specific.

 

[Donald Juan]

+ -
+ 50 0 50
- 20 30 50
70 30 100

TP=50, FP=0, FN=20, TN=30
Sen: 50/70=71%
Spec: 30/30=100%

Answer 3: Test is highly specific.

This

 

[mcloaf]

This shouldn't be hard. Just write out the 2x2 table.

 

[dozer1]

Scientists want to investigate a new test for prostate cancer and compare it with the gold standard test. In a sample of 100 persons, 70 had a positive result using the gold standard test. While the new test resulted in 50 positive results. Which of the following sentence is correct if the 50 positive results were true positive?

1) The new test is high sensitive --> This is not true b/c you just missed extra 20 cases comparing to the gold standard
2) FP in the new test is more than the gold standard test --> It tells you straight that 50 cases detected are true positives. so there are no FPs
3) The nest is high specific
4) The sensitivity of the test is 50%--> Not true since SN=TP/all with dz = 50/70

Just the way I think about it.

 

[stronghold]

Thanks guys. So you assumed that the 70 positive results of the gold standard are true diseased patients? Probably this the trick that made me confused

 

[CaliAtenza]

I dont understand how you get the FN value. I understand that they are saying that TP's are 50. And that in the gold standard, 70 people out of 100 have the disease, which would make the TN 30, as 30 people dont have the disease. I made the 2x2 table, but i am lost on the FN part.

 

[ButterfingerBBs]

70 people have the disease. 50 tested positive. therefore, 20 people who have the disease did not test positive. there are 20 false negatives.

 

[Donald Juan]

Thanks guys. So you assumed that the 70 positive results of the gold standard are true diseased patients? Probably this the trick that made me confused

Yes, you have to consider the gold standard to be true diseased patients. Even if it isn't 100% accurate, it's the best option you have to find the true value, and even if it isn't 100% accurate C is still the best answer.