Statistics

Question 1

What is sensitivity?

Answer 1

Proportion of people who have the disease who are correctly identified by a +ve test.

Question 2

What is specificity?

Answer 2

Proportion of those who do not have the disease who are correctly identified by a -ve test.

Question 3

What is the positive predictive value?

Answer 3

Proportion of those who test positive who actually have the disease.

Question 4

What is the negative predictive value?

Answer 4

Proportion of those who test negative who actually do not have the disease.

Question 5

What is the yield of a screening test?

Answer 5

The number of previously undiagnosed cases picked up by a screening programme.

Question 6

What is the yield of a screening test affected by?

Answer 6

Test characteristics, prevalence, recall period, uptake.

Question 7

What are the 7 criteria for screening?

Answer 7

1. Common/serious condition.
2. Well defined latent period where natural history of illness is well understood.
3. Suitable test available that is sensitive and specific.
4. Must be effective treatment.
5. Early detection improves prognosis, compared to waiting until symptoms present before treating.
6. Harm of screening small.
7. Cost justified, as competition for limited resources.