Measuring the effectiveness of screening

Question 1

Definition of sensitivity in screening

Answer 1

the proportion of people with the disease who are correctly identified by the screening test

Question 2

definition of Specificity in screening

Answer 2

the proportion of people without the disease who are correctly excluded by the screening test

Question 3

what are the 3 types of prevention

Answer 3

Primary
secondary
tertiary

Question 4

which type of prevention is used for no disease

Answer 4

primary

Question 5

what type of prevention is used for no symptoms

Answer 5

secondary

Question 6

what type of prevention is used for a clinical disease

Answer 6

Teriary

Question 7

Trying to detect a suspected disease with no symptoms yet such as breast cancer would be which level of prevention

Answer 7

secondary

Question 8

3 main aims of screening

Answer 8

provide treatment

reduce the risk of developing the disease

provide statistical data

Question 9

Define positive predictive value (PPV)

Answer 9

proportion od those who test positive and actually have the disease i.e predictive value of a true positive

Question 10

Define negative predictive value

Answer 10

the proportion of those who test negative and do not have the disease, i.e value of true negative

Question 11

List the criteria for screening

Answer 11

condition
treatment
Test
Risk/reward

Question 12

for the criteria ‘condition’ what must be considered in screening

Answer 12

should be an important health problem

history of condition should be well understood

condition should be able to be detectable early on in the progression

Question 12

for the criteria ‘treatment’ what must be considered in screening

Answer 12

should be treatment available for the condition

facilities to diagnose the conditions should be available

Adequate health service provision should be made for the extra clinical workload resulting from screening

Question 13

for the criteria ‘testing’ what must be considered in screening

Answer 13

suitable tests for early detection

the test should be acceptable

intervals for repeating tests should be determined

Question 14

for the criteria ‘risk/benefit’ what must be considered in screening

Answer 14

policy of who to treat

cost should be balanced with benefits

benefits should outweigh physical and psychological risks

Question 15

most ideal test for screening

Answer 15

RCT

Question 16

why can selection bias be an issue in screening

Answer 16

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

Question 17

what is lead-time bias

Answer 17

: When screening appears to increase survival time simply because the disease is detected earlier.

Once this is taken into account, there may be little or no effect of the screening test (i.e. improvement in survival time).

Patients may have the same lifespan as those detected earlier with screening and those detected when symptoms develop

Question 18

What is length time bias

Answer 18

An overestimation of survival because long-duration cases are more likely to be detected and treated than short-duration cases.

Question 19

List the 5 types of screening

Answer 19

Population-based screening
opportunistic screening
Screening for communicable diseases
Pre-employment and occupational medicals
Commercially provided screening