QuestionSBA
QuestionChoice
Based on the evidence given, the sensitivity of PSA testing is only 20%, which is not high. This means that some men with low PSA levels might still have prostate cancer. However, lowering the PSA cutoff level may worsen specificity and result in overdiagnosis
32047
e
The PSA level is a very sensitive test in diagnosing prostate cancer
QuestionChoice
There aree 100 true positives and 300 false positives = 400 total.The proportion of those men who actually have prostate cancer is 100 out of that 400 total, or 25%, which is the positive predictive value.

32046
d
1 in 5 people who test positive actually turn out to have prostate cancer
QuestionChoice
The specificity is defined as the proportion of people who test negative among all those who actually do not have the disease. It is calculated as (True negatives)/ (True negatives + False positives) = 1200/ (1200 + 300) = 80%.

The value of 20% is referring to the sensitivity of the test
32044
b
The specificity of the PSA test is 20%
QuestionChoice
The PPV is calculated as (True positives)/(True positives + False positives) = 100/ (100 + 300) = 25%. The value of 75% is referring to the negative predictive value
32045
c
The positive predictive value (PPV) of the PSA test is 75%
QuestionChoice
There aree 100 true positives and 300 false positives = 400 total.The proportion of those men who actually have prostate cancer is 100 out of that 400 total, or 25%, which is the positive predictive value.

32043
a
1 in 4 people who test positive actually turn out to have prostate cancer
Concept
Chapter
# Overview 

Several key parameters can be calculated to help describe how effective a certain test is at diagnosing a condition.

|                    | Patients with colon cancer | No cancer |
| ------------------ | :------------------------: | --------: |
| Biomarker positive |             a              |         b |
| Biomarker negative |             c              |         d |

# Sensitivity

Sensitivity is the proportion of people with the condition who will have a positive result. If, for example, the sensitivity of a test is 80%, out of a hundred people with the condition, only 80 will have a positive test result.

Sensitivity = a/(a+c)

# Specificity

Specificity describes the proportion of people without the disease who will have a negative test. A specificity of 90% can be interpreted as, out of 100 people without the disease, 90 will have a negative test result.

Specificity = d/(b+d)

# Positive Predictive Value

Positive predictive value (PPV) is the proportion of people with a positive test who actually have the disease. PPV varies with prevalence of disease in a population. The lower the prevalence, the lower the positive predictive value. A PPV of 78% will mean that if 100 people tested positive, 78 people will have the disease.

PPV = a/(a+b)

# Negative Predictive Value

Negative predictive value (NPV) is the proportion of people with a negative test who truly do not have the disease.

NPV varies with prevalence of disease in a population. The lower the prevalence, the higher the negative predictive value. An NPV of 97% will mean that if 100 people tested negative, 97 people will not have the disease.

NPV = d/(c+d)

# False positive rate

The false positive rate is the proportion of those without the condition who will test positive.

False positive rate = 1 - specificity

False negative rate = 1 - d/(b+d)

# False negative rate

The false negative rate is the proportion of those with the condition who will test negative.

False negative rate = 1 - sensitivity

False negative rate = 1 - a/(a+c)

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Evaluation of a diagnostic test
Topic
51
Medical Statistics
6409
Positive Predictive Value (PPV) is the probability that a positive test result accurately reflects the presence of a disease, calculated as TP/(TP + FP). Higher PPV indicates greater test reliability.
A 70-year-old retired statistician attends his General Practitioner's surgery for a routine medical checkup. He has done some reading online and would like to ask for advice on the utility of prostate specific antigen (PSA) testing to determine his likelihood of prostate cancer.

He has found a study in a population of 2000 males above 60 years old evaluating the prostate cancer detection rate using a PSA cut off of 4.0ng/mL. The data are as follows:

|               | Disease present | Disease absent |
| ------------- | --------------- | -------------- |
| Positive test | 100             | 300            |
| Negative test | 400             | 1200           |

Which of the following is true based on the evidence above?
a