A new rapid blood test was created to test for human papillomavirus (HPV) in a rural clinic. The following is a 2 × 2 chart that describes the results of the test. Answer questions 1–7 using the 2 × 2 chart.
| HPV | No HPV | Totals | |
| Positive Test | 95 | 37 | 132 |
| Negative Test | 39 | 278 | 317 |
| Totals | 134 | 315 | 449 |
1.What is the sensitivity of this test?
- What is the specificity of this test?
- What is the positive predictive value?
- What is the negative predictive value?
- Describe in words the sensitivity of this test.
- Describe in words the negative predictive value.
- What is the disease prevalence in this population?
- The sensitivity of this test can be calculated by dividing the number of true positive results by the total number of individuals with the disease (HPV). In this case, the number of true positives is 95, and the total number of individuals with HPV is 134. Therefore, the sensitivity is calculated as:
Sensitivity = (True Positives / Total with Disease) * 100 = (95 / 134) * 100 ≈ 70.90%
The sensitivity of this test is approximately 70.90%.
- The specificity of this test can be calculated by dividing the number of true negative results by the total number of individuals without the disease (No HPV). In this case, the number of true negatives is 278, and the total number of individuals without HPV is 315. Therefore, the specificity is calculated as:
Specificity = (True Negatives / Total without Disease) * 100 = (278 / 315) * 100 ≈ 88.25%
The specificity of this test is approximately 88.25%.
- The positive predictive value (PPV) of this test can be calculated by dividing the number of true positive results by the total number of positive test results. In this case, the number of true positives is 95, and the total number of positive test results is 132. Therefore, the PPV is calculated as:
PPV = (True Positives / Total Positive Test Results) * 100 = (95 / 132) * 100 ≈ 71.97%
The positive predictive value of this test is approximately 71.97%.
- The negative predictive value (NPV) of this test can be calculated by dividing the number of true negative results by the total number of negative test results. In this case, the number of true negatives is 278, and the total number of negative test results is 317. Therefore, the NPV is calculated as:
NPV = (True Negatives / Total Negative Test Results) * 100 = (278 / 317) * 100 ≈ 87.71%
The negative predictive value of this test is approximately 87.71%.
- The sensitivity of this test represents the proportion of individuals with the disease (HPV) who are correctly identified as positive by the test. In other words, it measures how well the test detects true positive cases out of all the individuals who actually have the disease. In this case, the sensitivity is approximately 70.90%, indicating that the test has a moderate ability to correctly identify individuals with HPV.
- The negative predictive value (NPV) of this test represents the proportion of individuals without the disease (No HPV) who are correctly identified as negative by the test. In other words, it measures how well the test rules out the presence of the disease in individuals who do not have it. In this case, the NPV is approximately 87.71%, indicating that the test has a high ability to correctly identify individuals without HPV.
- The disease prevalence in this population can be calculated by dividing the total number of individuals with the disease (HPV) by the total number of individuals in the population. In this case, the total number of individuals with HPV is 134, and the total number of individuals in the population is 449. Therefore, the disease prevalence is calculated as:
Prevalence = (Total with Disease / Total Population) * 100 = (134 / 449) * 100 ≈ 29.84%
The disease prevalence in this population is approximately 29.84%.