M12 Homework Assignment Please provide your answers to the following questions i
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Question
M12 Homework Assignment Please provide your answers to the following questions in a separate typed document. Include the question number with your answer and show all of your work for full credit. Answer questions 1-5 by referring to the following scenario. A recent nationwide study investigated the value of the prostate-specific antigen (PSA) blood test for the detection of prostate cancer among 100,000 men 50 years of age and older. Of the 686 men who tested positive on the PSA test, a total of 281 were ultimately diagnosed with prostate cancer, either by immediate needle biopsy or during 12 months of watchful waiting. An additional 45 men who tested negative on the PSA test were ultimately diagnosed with prostate cancer during 12 months of follow-up. 1) Set up the 2X2 contingency table for the data. 2) What is the sensitivity of the PSA test? Interpret the result. 3) What is the specificity of the PSA test? Interpret the result. 4) What is the positive predictive value (PPV) of the PSA test? Interpret the result. 5) What is the negative predictive value (NPV) of the PSA test? Interpret the result. Answer questions 6-10 by identifying the type of bias being described in each scenario. 6) A screening test is available to identify individuals with a genetic mutation that puts them at greater risk for stroke. The test is extremely expensive and is not covered by most insurance plans, so those choosing to have the test usually have to pay for it out-of-pocket. However, it has been determined that the screening test is very valuable because the annual incidence of stroke among those who have been screened is nearly half that of the general population. 7) One major benefit of mammography screening for breast cancer is that the disease is often diagnosed in the presymptomatic phase of the disease, before it is detectable by any other means, and breast cancers diagnosed in such early stages respond better to treatment. Another benefit of screening is that women diagnosed with breast cancer by way of mammography have better survival rates than women diagnosed by other means. 8) The prognosis for neuroblastoma, a tumor that occurs in young children, varies greatly by patient. Some tumors are slow-growing and may even heal spontaneously. Others tumors are fast-growing and aggressive. A urine screening test for neuroblastoma is currently available that detects metabolites produced by the tumor. It has been suggested that such screening is highly valuable PH20001 Essentials of Epidemiology 1 because the case-fatality rate of neuroblastoma among children diagnosed with the urine test is much lower than it is for those who were not screened. 9) Suppose that a new screening test has recently been developed to aid in the early identification of individuals with rheumatoid arthritis. However, the value of the test has not yet been established. In an effort to test the effectiveness of the new test in predicting a future diagnosis of rheumatoid arthritis, investigators enroll a group of volunteer participants, record their test result, and follow them forward for the development of the condition. It is subsequently determined that the new screening test is highly effective in predicting a definitive diagnosis of rheumatoid arthritis because the incidence of the condition among those who screened positive was much higher than that of the general population. 10) There are at least a dozen types of human papillomaviruses (HPV) that are considered high-risk and cause approximately 5% of all cancers world-wide. However, high-risk HPV infections are common and most occur without any symptoms and resolve on their own within 1-2 years. In 2003, cervical HPV screening tests became available and are now approved for use in combination with a Pap test among women over the age of 30. Such tests can detect infection of several high-risk HPV types before cell changes become evident. Some argue that HPV screening tests should be approved for universal use among women of all ages because the incidence of high-risk HPV infections has increased dramatically over the past decade. PH20001 Essentials of Epidemiology 2
Explanation / Answer
1) Set up the 2X2 contingency table for the data.
Total number of men = 100000
Number of men who tested postive = 686
Number of men who tested postive and have prostate cancer = 281
So, Number of men who tested postive and do not have prostate cancer = 686 - 281 = 405
Number of men who tested negative = 100000 - 686 = 99314
Number of men who tested negative and have prostate cancer = 45
Number of men who tested negative and do not have prostate cancer = 99314 - 45 = 99269
The contingency table is,
2) What is the sensitivity of the PSA test? Interpret the result.
Sensitivity = (A/A+C) * 100 = (281/281+45) * 100 = 86.2 %
If there is disease then there is 86.2% chance that the test is positive.
3) What is the specificity of the PSA test? Interpret the result.
Specificity = (D/D+B) * 100 = (99269/99269+405) * 100 = 99.6 %
If the men do not have the disease then there is 99.6% chance that the test will be negative.
4) What is the positive predictive value (PPV) of the PSA test? Interpret the result.
PPV = (A/A+B) * 100 = (281/281+405) * 100 = 40.96 %
If the test is positive then there is 40.96% chance that there is a disease.
5) What is the negative predictive value (NPV) of the PSA test? Interpret the result.
NPV = (D/D+C) * 100 = (99269/99269+45) * 100 = 99.95 %
If the test is negative then there is 99.95% chance that there is no disease.
Disease No Disease Total Positive 281 (A) 405 (B) 686 Negative 45 (C) 99269 (D) 99314 Total 326 99674 100000Related Questions
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