CSIM 2.1 Diagnostics 1 Interpreting Tests

Question 1

100% Sensitivity

Answer 1

Test will find 100% cases of disease, but will also have false positives. If a test has good sensitivity, good to exclude presence of disease

Question 2

100% Specificity

Answer 2

All those who haven’t got disease would get a negative result, but will be false negatives. If a test has good specificity, good to rule in presence of disease

Question 3

Sensitivity

Answer 3

True positive rate = TP/(TP+FN)

Question 4

Specificity

Answer 4

True negative rate = TN/ (TN+FP)

Question 5

positive predictive value

Answer 5

TP/(TP+FP) % of people with positive results who had disease

Question 6

Negative predictive value

Answer 6

TN/(TN+FN) % of people with negative results who didn’t have disease

Question 7

Likelihood Ratio

Answer 7

likelihood of result meaning disease vs no disease. Independent of population composition. Best measure of test performance

Question 8

Positive Likelihood ratio

Answer 8

TP rate/FP rate or Sensitivity/ 1-Specificity. Value of 1 means test useful. Criteria of 10 to be good test

Question 9

Negative Likelihood Ration

Answer 9

FN rate/TN rate or 1- Sensitivity/ Specificity. Value of 1 means test useful. Criteria of 0.1 to be good test

Question 10

ROC curves

Answer 10

ROC Slope: Likelihood ratio (LR)

ROC Area: Discriminatory power of test