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Book/movie review
22/08/2022
You have been asked to assess a new PCR test for the detection of bovine viral diarrhea (BVD) in beef cattle. The test manufacturers are marketing their test for use on pooled ear-notch samples; this strategy is proposed to be a more cost effective way for a producer to determine if his/her herd is positive because less testing is required and samples can be collected by the producer without a veterinarian present. Using the new PCR, you test pooled ear-notch samples from 97 beef herds in your region with no clinically-apparent BVD. You also collect individual animal blood samples from 20% of the cows in each herd (average number of cows sampled per herd: 13); you test the blood samples using an AC-ELISA test with sensitivity of 94.6% and specificity of 96.4%, and classify a herd as positive if at least one cow from the herd tests positive on the AC-ELISA test. According to the AC-ELISA tests, 68 herds were infected with BLV (one or more individual test positive animals). The pooled ear-notch PCR identifies 77 of the herds as positive, including 11 that were not considered positive on AC-ELISA. 1) Calculate the sensitivity and specificity of pooled ear notch PCR, using the AC-ELISA results as your gold standard. Please show your work. 2) Initially your gold standard for pooled ear notch PCR was AC-ELISA tests on individual animals, and herds were classified as infected if at least one cow tested positive on AGID. If you changed your gold-standard definition, classifying a herd as infected if at least two cows tested positive on AC-ELISA, how might that affect your evaluation of the ear-notch PCR 3) Assume that about 15% of the 500 herds in your region are infected with BVD a. What would the predictive value of a pooled ear-notch PCR test be for the region? b. What is the probability that a herd testing negative in your region is actually uninfected?
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The writer is very fast, professional and responded to the review request fast also. Thank you.
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