Sensitivity, Specificity, PPV, NPV These 4 measures describe how well diagnostic tests capture the true presence or absence of disease Sensitivity (SN) % with disease who test positive = a/(a+c) = TP/(TP+FN) Specificity (SP) % without disease who test negative = d/(b+d) = TN/(FP+TN) Positive predictive value (PPV) % positive test results that are true positives = a/(a+b) = TP/(TP+FP) Negative predictive value (NPV) % negative test results that are true negatives = d/(c+d) = TN/(FN+TN) Cut-off point may be adjusted to optimize sensitivity and specificity, which are inversely related (cut-off point with decreased sensitivity is associated with increased specificity and vice-versa) will also affect NPV and PPV i.e., decrease in sensitivity associated with decrease in NPV in the same population (due to higher false negative rates) Sensitivity and specificity are intrinsic to the diagnostic test do not change with prevalence PPV and NPV do change with prevalence Receiver operating characteristic (ROC) curves are a graphical depiction of a test's performance Y axis: sensitivity X axis: 1-specificity The higher the curve, the better the test This is quantified by the AUC (area under the curve); an AUC of 0.5 states that the test performs no better than chance (bad test!), whereas an AUC of 0.9 suggests a better-performing test Odds Ratio, Relative Risk, Attributable Risk These measures describe the relationship between a risk factor and a disease Odds Ratio (OR) odds of having disease in expose group / odds of having disease in unexposed group = ad/bc Relative Risk (RR) probability of getting disease in exposed group / probability of getting disease in unexposed group = [a/(a+b)] / [c/(c+d)] If RR = 1, there is no association between exposure and outcome Dose-repons'increased level of exposure shows an increased relative risk of developing/odds ratio of having a diseasecan be used in OR or RR to support causality increased level of exposure shows an increased relative risk of developing/odds ratio of having a disease can be used in OR or RR to support causality Attributable Risk (AR) risk in exposed group - risk in unexposed group = a/(a+b) - c/(c+d)
QUESTIONS 1 of 11 1 2 3 4 5 6 7 8 9 10 11 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M2.OMB.18.1) Health officials are considering a change be made to the interpretation of the tuberculin skin test that will change the cut-off for a positive purified protein derivative (PPD) from 10 mm to 15 mm for healthcare workers. Which of the following can be expected as a result of this change? QID: 210446 Type & Select Correct Answer 1 Decrease the sensitivity 50% (18/36) 2 Decrease the specificity 11% (4/36) 3 Increase the precision 3% (1/36) 4 Increase the sensitivity 25% (9/36) 5 No change to the sensitivity or specificity 6% (2/36) M 5 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M2.OMB.18.1) A home drug screening test kit is currently being developed. The cut-off level is initially set at 4 mg/uL, which is associated with a sensitivity of 92% and a specificity of 97%. How might the sensitivity and specificity of the test change if the cut-off level is changed to 2 mg/uL? QID: 210448 Type & Select Correct Answer 1 Sensitivity = 90%, specificity = 99% 25% (3/12) 2 Sensitivity = 92%, specificity = 97% 17% (2/12) 3 Sensitivity = 95%, specificity = 98% 8% (1/12) 4 Sensitivity = 97%, specificity = 96% 50% (6/12) 5 Sensitivity = 100%, specificity = 97% 0% (0/12) M 5 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK
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