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Screening Tests in Medical Diagnosis: Sensitivity, Specificity, and Predictive Values, Study Guides, Projects, Research of Pharmacology

University of Texas Health Science Center (UTHealth) - HoustonPharmacology

A comprehensive guide to understanding the concepts of sensitivity, specificity, positive predictive value (ppv), and negative predictive value (npv) in medical screening tests. It explores how these metrics are crucial for evaluating the effectiveness of diagnostic tools and their impact on patient care. Numerous examples and exercises to illustrate the application of these concepts in real-world scenarios, making it a valuable resource for students and professionals in the medical field.

Typology: Study Guides, Projects, Research

2024/2025

Available from 04/08/2025

Carter_Flinch
Carter_Flinch 🇺🇸

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Assignments PHM2612
Module 4. Measuring & Screening
Correct Answers
Complete this quiz on Canvas by or before the due date listed on the class calendar. You will
only have one attempt to complete the quiz; however, there is no time limit. Read each
question carefully and answer to the best of your knowledge. Please model requested
interpretations after the examples in the lecture. For questions requiring calculations, keep 5
decimal places for intermediate steps and round your final answers to two decimal places,
unless instructed otherwise. You may use this document to answer the questions prior to
submitting your responses on Canvas under the QUIZZES tab. (100 points)
1. As the 2022 Winter Olympics approached, the International Olympic Committee
wanted a screening test that would correctly identify a high proportion of athletes
who used illegal performance-enhancing drugs. On the other hand, the athletes were
concerned about a screening test that would incorrectly identify persons as using
illegal performance-enhancing drugs when, in fact, they were not using them. Which
of the following screening test characteristics were important to each group?
Complete the sentence below using the following options: specificity, sensitivity. (2
points)
Olympic officials wanted a test with high __Sensitivity__ .
Athletes that planned to compete in the games wanted a test with high
__Specificity__ .
2. If a test is reliable, then it is also valid. (1 point)
a. True
b. False
3. Using a test in a high prevalence population will result in an increase in the positive
predictive value of the screening test compared to when that same screening test is
used in a low prevalence population. (1 point)
a. True
b. False
pf3
pf4
pf5
pf8
pf9
pfa

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Assignments PHM Module 4. Measuring & Screening Correct Answers Complete this quiz on Canvas by or before the due date listed on the class calendar. You will only have one attempt to complete the quiz; however, there is no time limit. Read each question carefully and answer to the best of your knowledge. Please model requested interpretations after the examples in the lecture. For questions requiring calculations, keep 5 decimal places for intermediate steps and round your final answers to two decimal places, unless instructed otherwise. You may use this document to answer the questions prior to submitting your responses on Canvas under the QUIZZES tab. ( 100 points )

  1. As the 2022 Winter Olympics approached, the International Olympic Committee wanted a screening test that would correctly identify a high proportion of athletes who used illegal performance-enhancing drugs. On the other hand, the athletes were concerned about a screening test that would incorrectly identify persons as using illegal performance-enhancing drugs when, in fact, they were not using them. Which of the following screening test characteristics were important to each group? Complete the sentence below using the following options: specificity, sensitivity. ( points)  Olympic officials wanted a test with high Sensitivity.  Athletes that planned to compete in the games wanted a test with high Specificity.
  2. If a test is reliable, then it is also valid. (1 point) a. True b. False
  3. Using a test in a high prevalence population will result in an increase in the positive predictive value of the screening test compared to when that same screening test is used in a low prevalence population. (1 point) a. True b. False
  1. The specificity of a screening test depends on the prevalence of the disease in a given population. (1 point) a. True b. False
  2. The incidence of the targeted disease will likely increase during a given period after a new screening test becomes widely used for this disease. (1 point) a. True b. False
  3. Sensitivity answers the question: “Among all the individuals who have the disease, what proportion of the screening test results are positive for this disease?” (1 point) a. True b. False
  4. Successful treatment programs that shorten the duration of a disease primarily affect the incidence, but not the prevalence of this disease. (1 point) a. True b. False
  5. The preclinical phase of disease is the stage that occurs between the biological onset of disease to the point that symptoms of the disease first appear. Which type of prevention is best suited for this phase? (1 point) a. Primary b. Secondary c. Tertiary d. Quaternary
  6. A “gold standard” is used to determine whether a screening test is ______. (2 points) a. cost-effective b. valid c. reliable d. Valid and reliable e. All of the above
  1. A screening test is beneficial at the population level if: (2 points) a. The screening test is used in a population with a high prevalence of the disease. b. The screening test has a high sensitivity for identifying the condition. c. The screening test has a low frequency of false positives. d. A false negative result with this screening test will not have an adverse health outcome for the patient or his/her close contacts. e. Choices a, b and d only f. All of the above
  2. Which of the following statements do NOT describe the Kappa statistic? (2 points) a. The Kappa statistic is a measure of reliability b. The Kappa statistic is a measure of validity. c. A Kappa value of > 0.75 represents excellent agreement. d. All of the above.
  3. Construct and label a generic 2x2 table in terms of True Positives (TP) /False Positives (FP) / True Negatives (TN) and False Negatives (FN). Hint: cell a, the top left cell should be TP for true positive, and do not forget to include titles and totals as well. Use words, not numbers. You may copy and paste your table directly from word. ( points). Disease Positive Disease Negative Total Screening Test Positive True Positives (TP) False Positives (FP) TP+FP Screening Test Negative False Negatives (FN) True Negative (TN) FN+TN Total TP+FN FP+TN TP+FP+FN+TN
  1. The prevalence of a disease is 22% in population X (n = 37,000). Two screening tests have been developed for this disease. Individuals first undergo screening test 1, which has a sensitivity of 80% and specificity of 75%. Only individuals who test positive from screening test 1 will then undergo the more invasive screening test 2 , which has a sensitivity of 95% and a specificity of 92%. HINT: do not use the prevalence for Table 1 to calculate numbers in the second table. Please complete the following contingency tables: (9 points). Screening Test 1 True Disease Status Total Positive Negative Test Result Positive 6512 7,215 13, Negative 1628 21,645 23, Total 8140 28,860 37, Screening Test 2 True Disease Status Total Positive Negative Test Result Positive 6186 577 6763 Negative 326 6638 6964 Total 6512 7215 13, Use the following information to answer questions 18-21. The following question is loosely based on data and methods from a study by Flores-Chavez, et al. (2012) on a new diagnostic tool for testing various parasitic diseases in Spain. Flores-Chavez, M., et al. 2012. “Sensitivity and Specificity of an Operon Immunochromatographic Test in Serum and Whole-Blood Samples for Diagnosis of Trypanosoma cruzi infections in Spain, an Area of non-endemicity.” Clin Vaccin Immunol. 19(9):1253-1359. Report your answer as a percentage rounded to the nearest hundredth for all questions in this series (i.e., 2 decimal points).
  1. Construct the appropriate 2x2 table with the information provided above (including labels for rows and columns). (10 points = 1 pt for each numeric cell and 1 pt for including all labels). True Characteristics of the Population Test + true pos - Total
  • 107 21 128
  • 19 235 254 Total 126 256 382
  1. Calculate the positive predictive value (PPV) of the screening test (round to 1 decimal place). (1 point) a/(a+b) = (107/128)*100 = 83.6%
  2. Choose the correct interpretation(s) for the PPV value calculated above. Check all that apply. (2 points) ☐ This test is able to correctly identify XX.XX% of those with malaria. ☒ Among the individuals that test positive for malaria, the proportion that actually have malaria is XX.XX%. ☐ XX.XX% of those who test negative for malaria actually do not have the disease. ☒ XX.XX% of those who test positive for malaria actually have the disease.
  3. Calculate the negative predictive value (NPV) of the screening test (round to 1 decimal place). (1 point) 236/255=92.
  4. Choose the correct interpretation(s) for the NPV value calculated above. Check all that apply. (2 points) ☐ This test is able to correctly identify XX.XX% of those without malaria. ☒ Among the individuals that test negative for malaria, the proportion that actually do not have malaria is XX.XX%. ☒ XX.XX% of those who test negative for malaria actually do not have the disease. ☐ XX.XX% of those who test positive for malaria actually have the disease.

Questions 27-29 refer to a second new screening test that was assessed in a subset of 50 participants with malaria and 120 participants without malaria from the scenario described above. With this second test, 70% of those who have malaria had true positive results, and 75% of those without malaria had true negative results.

  1. Construct the appropriate 2x2 table with the information provided above (include labels for rows and columns). (10 points = 1 pt for each numeric cell and 1 pt for including all labels). True Characteristics of the Population Test Disease No Disease Total Positive 35 30 65 Negative 15 90 105 Total 50 120 (75% (^170)
  2. Calculate the sensitivity of screening test 2. Report your answer as a percentage rounded to the nearest hundredth (xx.xx). (2 points) 35/50=70%
  3. Based on the sensitivity and the specificity of the two tests, which of the 2 new tests would you want to use? Keep in mind that for this class, a difference of 10% or higher would have to be observed between two tests in order to consider that there is a better (or worse) performance than the other. (2 Points) a. Test 1 because both sensitivity and specificity are higher for test 1 b. Test 2, because both sensitivity and specificity are higher for test 2 c. Neither test has an advantage based on sensitivity and specificity d. Based on sensitivity only, test 1 is better e. Based on specificity only, test 1 is better Use the following table to answer questions 30-38. The authors of a study wanted to assess the accuracy of a questionnaire used to diagnose depression. They selected a random set of elderly residents living at an assisted facility and used medical records to determine who did and did not have depression, which had been assessed upon arrival at the facility and regularly thereafter. This medical record assessment served as a “gold standard” for the analysis. The table below shows the data from the subgroup analysis. For the following calculations, report your answers as a percentage rounded to the nearest hundredth (xx.xx%). Results of the depression questionnaire

c. Sensitivity and PPV d. Overall Agreement and True Positives Use this information to answer questions 39-43. A hospital is training radiologists to read chest x-rays to diagnose tuberculosis (TB). To determine how well the new radiologist is doing, his results are compared to those of a radiologist with 20 years of experience. The results are tabulated below. Report your answers as a percentage rounded to the nearest hundredth (e.g., 25.325% = 25.33%). 20-year veteran Total TB Disease No Disease Newbie TB Disease 405 288 693 No Disease 232 807 1039 Total 637 1095 1732

  1. Calculate the overall percent agreement between the two radiologists. Provide your answer as a percent (%). (2 points) 1212/1732=69.98%
  2. Suppose the overall agreement above is 59%, choose the correct interpretation(s) for the overall agreement. (2 points) a. The agreement is good between the two radiologists. Therefore, the test is valid. b. 59% of the population with or without tuberculosis infection will be diagnosed incorrectly, regardless of who reads the x-rays. c. Among the TB disease cases, 59% of those read by the new radiologist agreed with the veteran. d. The radiologists agreed on 59% of all the results.
  3. Calculate the expected agreement based on chance alone. Keep 5 decimal places for intermediate steps. Provide your answer as a percent (%). (1 point) 52.64%
  4. Calculate the kappa statistic using the values reported from Q39 and Q41 (XX.XX%). Please keep 5 decimals for all intermediate steps. Report your final answer as a

decimal rounded to the nearest hundredth (e.g., 0.XX) - do NOT convert to a percent. (2 points) .

  1. Interpret the Kappa statistic calculated in the previous question using the Landis & Koch criteria. (2 points) a. Excellent agreement b. Fair agreement c. Good agreement d. Poor agreement