Using the Evidence - Lecture Thirty-Five

Question 1

Screening

Answer 1

The widespread use of a simple test for a disease in an apparently healthy population

Question 2

Screening programme

Answer 2

An organised system using a screening test among healthy people in the population to identify early cases of disease in order to improve outcomes

Question 3

Screening test

Answer 3

Usually cheap, simple

Question 4

Why try to detect disease early?

Answer 4

Limit the consequences of disease through early diagnosis and treatment

Question 5

Screening

Answer 5

Aims to improve outcomes usually to reduce mortality

Question 6

Long lead time =

Answer 6

Greater chance of detecting disease early

Question 7

Critical Point One of Screening

Answer 7

Disease is not detectable

Question 8

Critical Point Two of Screening

Answer 8

Screening may be of benefit

Question 9

Critical Point Three of Screening

Answer 9

Usually diagnosed anyway - no benefit

Question 10

Over-diagnosis

Answer 10

Someone might have an illness but not be the cause of their death

Question 11

Intrinsic Test

Answer 11

Measures accuracy with sensitivity and specificity

Question 12

Sensitivity

Answer 12

Proportion of people with the disease who test positive

Question 13

Specificity

Answer 13

Proportion of people without the disease and test negative

Question 14

Specificity limitations

Answer 14

Costs and risks of next step high

Question 15

Sensitivity benefits

Answer 15

Detecting as many cases as possible important

Costs or risks of next step not too high

Question 16

Sensitivity & Specificity

Answer 16

What proportion of people with or without disease the test correctly classifies

Question 17

Predictive Values

Answer 17

What proportion of people who test positive/negative do/don’t have disease

Question 18

Positive Predictive Value (PPV)

Answer 18

Proportion of people who test positive and have the disease

Question 19

Negative Predictive Value (NPV)

Answer 19

Proportion of people who test negative and don’t have the disease

Question 20

Predictive Values

Answer 20

Influenced by disease prevalence in the population of interest, unlike sensitivity and specificity

Question 21

Facilities and Systems

Answer 21

Manage participation
Cost and accessibility
Quality control and monitoring

Question 22

Treatment

Answer 22

Capacity to treat true positives

Question 23

Cost effectiveness

Answer 23

Many people over long period

Cost vs benefit

Question 24

Evaluation of screening programmes

Answer 24

Crucial to determine if screening programme actually leads to benefit

Question 25

Benefits of screening programmes

Answer 25

Potential for early detection and intervention
Reassurance (true negatives)
Improved health of population

Question 26

Potential for early detection and intervention

Answer 26

Reduced mortality and/or morbidity

Possibly less radical treatment required

Question 27

Physical harms of screening programmes

Answer 27

From complications, invasive tests and/or treatments

Question 28

Psychological harms of screening programmes

Answer 28

From anxiety from waiting, distress from invasive tests or procedures, knowing about serious diagnosis for longer, false negative or false positive results

Question 29

Financial harms of screening programmes

Answer 29

To individual and health service

Question 30

Harms of screening programmes

Answer 30

Lead time bias

Length bias

Question 31

Lead time bias

Answer 31

Over-diagnosis and/or over-treatment- may increase morbidity without reducing mortality

Question 32

Length bias

Answer 32

False positives - period of stress and uncertainty until diagnostic test
May diagnose a disease that would never have become apparent