# Chapter 1-statistics.txt

 What is the minimum # of subjects required to establish a reference interval? (according to this text) 60 Reference limits for data showing a normal distribution are calculated values representing what? Mean+/- 2 SD What is the likelihood of one value falling outside the Ref. Int? (1-0.95n)x100 T/F: Reference intervals represent results expected in all healthy animals. F represents expected results in 95% of healthy animals "Why is ""reference range"" and inappropriate term?" b/c statistically it means the difference b/w the high and low values T/F: Analytical precision is the ability of an assay to get the same result if the same sample is analyzed several times T "Calculate the CV for the following diagnostic tests. Test A: Mean=10, SD=3, Test B: Mean=50, SD=4" "A:30%, B:8%" CV=(SD/Mean)x100 Which test is more precise? B low CV-> high prec T/F: Within-assay CV represents random error w/in a run of the assay and the error from additional runs of the assay on the same sample. F That is between-assay CV "If a clinical decision is based on a minimal change in the value of an analyte, should the CV be high or low?" Low What term represents the ability of a test to produce a change in the signal for a defined change of the quantity? Analytical Sensitivity Define accuracy. the closeness of the agreement b/w the measured value and the true value Define analytical specificity ability to detect only the substance of interest freedom from interference T/F: A test w/ high diagnostic specificity is a good screening test. "F, screening tests should have high sensitivity" A test w/ high diagnostic sensitivity has few (FN/FP) results. Choose one FN Define positive predictive value. the probablitiy that a positive test indicates that the animal has the disease PPV=TP/(TP + FP) "When prevalence is low, which is more likely to occur? FN or FP" FP A test with few FN compared to TN results has a high (PPV/NPV). Choose one. NPV NPV=TN/(TN +FN) T/F: The clinical value of the calculated diagnostic properties is influenced by prevalence. T PPV is less when the disease prevalence is (high/low). Choose low "Disease prevalence=10%, n=1000, sensitivity=94%, specificity=85%. Calculate TP, FP, TN, FN, PPV and NPV" "TP=94, FP=135, TN=765, FN=6, PPV=41%, NPV=99%" What happens to the PPV when the prevalence increases to 25%? It increases b/c TP increase and FP decrease AuthorAnonymous ID29661 Card SetChapter 1-statistics.txt DescriptionChapter 1 Updated2010-08-12T01:49:46Z Show Answers