You learned the basics of outbreak investigation in Module 1, and additional measures of disease occurrence and approaches to measuring and monitoring disease frequency in this module. Consider how descriptive epidemiology and surveillance are important and useful tools to identify and track trends in disease occurrence, and the basic measures of disease frequency that are used. Remember, epidemiologists count! They ‘count’ in that they make a difference in the world of public health. They also literally count because they measure disease frequency – and then interpret. Think about how visualizing data is an important aspect of this process.
In a MS Word or similar document, with each question numbered, respond to each of the questions below.
Disease Status
Screening Status Sick Healthy Total
Positive 78 792 870
Negative 22 9,108 9,130
Total 100 9,900 10,000
1. Using these data (above), calculate the following and interpret the results in a sentence.
a. Sensitivity
b. False Negative Rate
c. Specificity
d. False Positive Rate
e. Positive Predictive Value
f. Negative Predictive Value
g. Prevalence of Disease
Disease Status
Screening Status Sick Healthy Total
Positive 640 1,400 2,040
Negative 360 7,600 7,960
Total 1,000 9,000 10,000
2. Using these data (above), calculate the following and interpret the results in a sentence.
h. Sensitivity
i. False Negative Rate
j. Specificity
k. False Positive Rate
l. Positive Predictive Value
m. Negative Predictive Value
n. Prevalence of Disease
3. Based on your answers to # 1 and # 2, which of the two tests is the most accurate? Why? Which of the two tests performs better, that is, yields the greatest proportion of cases in the population screened? Why?
4. Which test, A or B, would you rather have as a screen for HIV in the U.S. population? Why? Would your answer be the same in a different population? Why or why not?
5. A study was conducted examining a new test for determining carpal tunnel syndrome. Due to the repetitive work that auto assembly line workers face when assembling cars, these workers were recruited into the study. The new test examines nerve conduction (NC) to determine carpal tunnel syndrome. NC screens were performed on 1,200 workers. 650 had symptoms of carpal tunnel syndrome. Of these, 523 had abnormalities on NC tests consistent with carpal tunnel syndrome. Of those without symptoms, 187 had abnormalities consistent with the diagnosis of carpal tunnel syndrome. Assuming that the symptoms of carpal tunnel syndrome are the gold standard for diagnosis, construct a 2×2 table and answer the following:
o. Calculate and interpret the sensitivity of the NC test.
p. Calculate the true prevalence of carpal tunnel syndrome.
q. Your initial study was a multi-center trial in North America. You want to know how the test will perform in Japan, where the prevalence of carpal tunnel syndrome is lower compared to the North American population. What happens to the positive predictive value of your test when you re-run the study in Japan?