Screening test statistics

Question 1

Sensitivity

Answer 1

Proportion of patients with the condition who have a positive test result

TP / (TP + FN )

Question 2

Specificity

Answer 2

Proportion of patients without the condition who have a negative test result

TN / (TN + FP)

Question 3

The chance that the patient has the condition if the diagnostic test is positive

Answer 3

Positive predictive value

TP / (TP + FP)

Question 4

The chance that the patient does not have the condition if the diagnostic test is negative

Answer 4

Negative predictive value
TN / (TN + FN)

Question 5

How much the odds of the disease increase when a test is positive

Answer 5

Likelihood ratio for a positive test result

sensitivity / (1 - specificity)

Question 6

How much the odds of the disease decrease when a test is negative

Answer 6

Likelihood ratio for a negative test result
(1 - sensitivity) / specificity

Question 7

Wilson and Junger criteria

Answer 7

1. The condition should be an important public health problem
2. There should be an acceptable treatment for patients with recognised disease
3. Facilities for diagnosis and treatment should be available
4. There should be a recognised latent or early symptomatic stage
5. The natural history of the condition, including its development from latent to declared disease should be adequately understood
6. There should be a suitable test or examination
7. The test or examination should be acceptable to the population
8. There should be agreed policy on whom to treat
9. The cost of case-finding (including diagnosis and subsequent treatment of patients) should be economically balanced in relation to the possible expenditure as a whole
10. Case-finding should be a continuous process and not a ‘once and for all’ project