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University Of Arizona *

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376

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Mechanical Engineering

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Jan 9, 2024

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4

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BME 376: Assignment E This assignment is focused on diagnostic tests. All answers should be entered in the space provided below each question. Most/each sub-question(s) will be graded as 1 (complete) or 0 (incomplete). Upload a completed word or PDF document to D2L. Type equations (using in-built Word features) and text. Avoid screenshots or images. You may use the following equation (based on Bayes’ theorem) as the basis for this assignment. Positve PredictiveValue = Sensitivity Prevalence Sensitivity Prevalence + ( 1 Specificity ) ( 1 Prevalence ) 1. Cervical cancer is a disease for which the chance of containment is high given that it is detected early. The Pap Smear is a widely accepted screening procedure that can detect cervical cancer; it has been credited with being primarily responsible for the decreasing death rate due to cervical cancer in recent years. The sensitivity and specificity of Pap Smear are 83.75% and 81.36%, respectively. The prevalence of cervical cancer among women is 8.3 cases per 100,000 women. 1.1. [2 points] Compute the positive predictive value of the test 1.2. [2 points] Compute the negative predictive value of the test 1.3. [2 points] Comment on the predictive values. 1
What would you suggest if the test turns out to be positive? What would you suggest if the test turns out to be negative? 2. A “Gold Standard” procedure is available to detect whether or not a person has tuberculosis (TB). Chest X-rays are routinely used as an alternative simple inexpensive procedure to detect the presence or absence of the disease in individuals. We would like to evaluate how good the X-rays are as diagnostic tools. A sample of 30 people, who are known to have tuberculosis, are given a chest x-ray. Another sample of 1,790, who are known not to have tuberculosis, are also given a chest x-ray. The results are summarized below. X-ray Tuberculosis Yes No Negative 8 1739 Positive 22 51 (a) [4 points] Estimate the sensitivity and specificity of chest X-rays in detecting TB. (b) [4 points] In USA, 9.3 people out of 100,000 have tuberculosis. Compute the predictive value of a positive Test and predictive value of a negative test. 2
(c) [2 points] Comment on the usefulness of chest X-rays as a diagnostic tool i.e., what would you suggest if the test turns out to be positive? What would you suggest if the test turns out to be negative? 3. The following data are from a study comparing self-reported smoking status with measured serum cotinine level. In this study, cotinine level was used as a screening tool for smoking status. For various cut-off points (for cotinine level), the observed sensitives and specificities are given below. Cotinine level (ng/mL) Sensitivity Specificity 5 0.971 0.898 7 0.964 0.931 9 0.960 0.946 11 0.954 0.951 13 0.950 0.954 14 0.949 0.956 15 0.945 0.960 17 0.939 0.963 19 0.932 0.965 a) [3 points] Determine the cut-off point that will yield the most optimal sensitivity and specificity for the cotinine levels as a screening test. 3
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b) [1 point] Cotinine levels can be measured in both saliva and urine. A study determined the AUC - area under the receiver operating characteristic (ROC) curve – was 0.958 and 0.973 for saliva and urine-based cotinine test, respectively. Based on the AUC, which test is more reliable? 4