Lecture 2: Screenings in Medicine Flashcards
Which 2 elements describe accuracy of test result?
Sensitivity and Specificity
Which 2 elements predicts accuracy of diagnosis?
- Positive predictive value
- Negative predictive value
What is the sensitivity of a screening test?
- How accurately a test can correctly detect presence of disease when in fact disease is actually (known to be) present
- % of time that a TEST is positive in a patient that is known to have the disease
How is the sensitivity calculated?
Sensitivity = TP / (TP + FN) x 100% or A / A+C
What is the specificity of a screening test?
How accurately a test can correctly detect absence of disease when in fact the disease is actually (known to be) absent
How is specificity of a test calculated?
Specificity = TN / (FP + TN) x 100% or B / B+D
How is positive predictive value (PPV) calculated?
PPV = TP / (TP + FP) x 100%orA / A + B
How is negative predictive value (NPV) calculated?
NPV = TN / (FN + TN) x 100%orD / C + D
What does diagnostic accuracy (DA) aka diagnostic precision (DP) represent and how is it calculated?
- % of all correctly-identified patients (TP’s and TN’s, collectively) out of the total (all) number of screened patients
- DA (DP) = (TP+TN) / (TP+FP+FN+TN)orA+D / (All Patients)
Which 2 values can sensitivity give us about a test?
True Positives and False Negatives
Which 2 values can specificity give us about a test?
True Negatives and False Positives
How is the likelihood ratio positive (LR+) calculated?
- Sensitivity / (1-specificity)
- [(A ÷ (A+C)) ÷ (B ÷ (B+D))]
What should the LR+ and LR- value be to demonstrate the test is most beneficial?
- LR+ >10
- LR- <0.1
How is the likelihood ratio negative (LR-) calculated?
- (1-sensitivty) / specificity
- [(C ÷ (A+C)) ÷ (D ÷ (B+D))]
