Screening

Question 1

What is screening?

Answer 1

A process that tests for a condition or disease in a population of apparently well people who are in a high risk population - purpose is PREVENTION

Question 2

What is primary prevention

Answer 2

Aims to prevent a disease from occuring

Question 3

What is secondary prevention

Answer 3

Detection of a disease in its early stages in order to alter the course of disease and maximise changes of complete recovery

Question 4

What is teritary prevention

Answer 4

Trying to slow down the progression of the disease

Question 5

What is a false positive?

Answer 5

When the result of a test is positive although the person does not actually have the disease

Question 6

What is a true positive?

Answer 6

When the result of the test s positive and the patient has the disease

Question 7

What is a false negative?

Answer 7

When the result of the test is negative but the patient actually has the disease

Question 8

What a true negative?

Answer 8

When the result of a test is negative, and this is correct because the patient does not have the diease

Question 9

What does the sensitivity of a screening programme measure?

Answer 9

The proportion of people with the disease who are correctly identified by the screening test
true positives/people with the disease

Question 10

What does the specificity of a screening programme measure?

Answer 10

The proportion of people without the disease who are correctly excluded by the test
true negative/population without the disease

Question 11

What is the positive predictive value (PPV) of a screening programme measure?

Answer 11

The proportion of people with a positive result who actually have the disease
true positive/positive results

Question 12

What is the negative predictive value (NPV) of a screening programme measure?

Answer 12

The proportion of people with a negative result who do not have the disease
true negatives/all negatives

Question 13

What is the result of a screening test with a low sensitivty

Answer 13

Not all patients with the disease will be identified

Question 14

What are the possible consequences of a screening programme with a low PPV

Answer 14

• patients potentially receive unnecessary diagnostic procedures
• may cause unnecessary anxiety as the test was positive but the patient DO NOT have the disease
• cost

Question 15

What is prevalence?

Answer 15

The proportion of a population found to have the disease

Question 16

What is incidence?

Answer 16

The number of new cases within a specified time period, divided by the population at risk

Question 17

What is the Wilson and Jungner criteria for screening? 
In terms of 
-the condition
-the treatment
-the test
-the benefits

Answer 17

THE CONDITION
a) it should be an serious health problem
b) the aetiology should be well undestood
iii there should be a detectable early stage

THE TREATMENT

a) there should be an accepted treatment for the disease
b) facilities for diagnosis and treatment should be available
c) there can’t be an unmanageable extra clinical workload

THE TEST

a) a suitable test should be devised for the early stage
b) the test should be acceptable for the patients
c) intervals for repeating the test should be determined

BENEFITS

a) there should be an agreed policy on whom to treat
b) the cost should be balanced against the benefits

Question 18

What selection bias?

Answer 18

People who choose to participate in screening programmes may be different from those who do not

Question 19

What is lead time bias?

Answer 19

Screening merely identifies the disease earlier than before and thus gives the impression that survival is prolonged (but survival time is unchanged)

Question 20

What is time-length bias?

Answer 20

Diseases that have a longer period of presentation are more likely to be detected by screening than the ones with shorter time of presentation