(6) Screening

Question 1

List at least six criteria to approve a screening system.

Answer 1

• Quick & cheap & acceptable to populations
• Serious health conditions
• Well known epidemiology and natural history
• Defined cut-off points of positives and negatives
• Defined people who to be screened for
• Already available effective preventive treatments
• Invasiveness of screening benefits > harms
• Early detection available

Question 2

What are: True positives, False positives, True negatives and False negatives?

Answer 2

• True positives = detected diseased people
• False positives = detected UN-diseased people
• True negatives = excluded un-diseased people
• False negatives = excluded DISEASED people

Question 3

What are Specificity and Sensitivity? How are they calculated?

Answer 3

• Sensitivity = proportion of DISEASED people who are tested positive; (True positives) / (True positives & False negatives)
• Specificity = proportion of UN-diseased who are tested negative; (True negatives) / (True negatives & False positives)

Question 4

What are the value of the following indicate?

• (True positives) / (True positives & False negatives)
• (True negatives) / (True negatives & False positives)

Answer 4

• Sensitivity

- Specificity

Question 5

What are True Predicted Value and False Predicted Value? How are they calculated?

Answer 5

• PPV = proportion of people who are tested positive are actually DISEASE; (True positives) / (True & False positives)
• NPV = proportion of people who are tested negative are actually UN-diseased; (True -ve) / (True & False -ve)

Question 6

What are the value of the following indicate?

• True positives) / (True & False positives)
• (True negatives) / (True & False negatives)

Answer 6

• True Predicted Value

- False Predicted Value

Question 7

Explain what is Lead Time Bias?

Answer 7

Patients actually have same life expectancy, but those screened detected earlier so seemed lived longer

Question 8

Explain what is Length Time Bias?

Answer 8

Screening is better at picking up non-threatening diseases, so life expectancy seemed longer if detected

Question 9

Explain what is Selection Bias?

Answer 9

Those chose to be screened are more likely to engage healthy behaviours.

Question 10

Define screening

Answer 10

• Systemic attempts
• Detect unrecognised conditions
• Those at high risks
• Cheaply & rapidly

Question 11

Suggest ways we might detect disease (3).

Answer 11

• Spontaneous presentations from patients seeing GPs
• Opportunistic detections when looking for something else
• Screening

Question 12

List the criteria for implementing a screening programme relating to the DISEASE (4).

Answer 12

• Serious (QoL or death)
• Well understood natural history & epidemiology
• Dearly detectable stage
• Cost-effective primary prevention available

Question 13

List the criteria for implementing a screening programme relating to the TEST (4).

Answer 13

• Quick
• Precise & valid
• Acceptable
• Defined cut-off positives/negatives

Question 14

List the criteria for implementing a screening programme relating to the TREATMENT (2)

Answer 14

• Early treatment must be advantageous

- Effectiveness

Question 15

List the criteria for implementing a screening programme relating to the PROGRAMME (4)

Answer 15

• Effective (RCT)
• Benefits > psychological harm
• Facilities for diagnosis & treatments
• Facilities for consolling

Question 16

What two types of error in the results do screening programmes make? What are some of the issues for the people with these errors?

Answer 16

• False positives: give stress, anxiety, unnecessary treatment, cost to diagnose them)
• False negatives: inappropriate reassurance leading to late presenting to be diagnosed

Question 17

How do you calculate the prevalence of a disease?

Answer 17

(True positives + False negatives) / (All values)

Question 18

Why can screening provide an issue for the doctor performing it? Compared to normal patient presentation)

Answer 18

If the patient presents with an issue and it is bad news then it’s a sad time, but the doctor has no involvement but helping them. However id and issue is picked up in screening then a doctor has actively gone out to tell you this.

Question 19

Suggest some sociological critiques of health promotion and screening (4).

Answer 19

• Structural: victims blame it become their responsibilities to check & why not do primary prevention to exposures
• Surveillance: is it a social control?
• Social construction: given meaning through particular social relationships, you should go to screening as it’s the right thing to do
• Female are more targeted to be screened?

Question 20

Give examples of screening programmes in the UK (9)

Answer 20

• Abdominal Aorta Aneurysm
• Breast Cancer
• Cervical Cancer
• Bowel Cancer
• Diabetic Retinopathy
• Down’s Syndrome
• Foetal Abnormalities
• Parkinson’s Disease
• Sickle Cell & Thalassaemia

Question 21

What type of bias is: Patients actually have same life expectancy, but those screened detected earlier so seemed lived longer

Answer 21

Lead time bias

Question 22

What type of bias is: Screening is better at picking up non-threatening diseases, so life expectancy seemed longer if detected

Answer 22

Length time bias

Question 23

What type of bias is: Those chose to be screened are more likely to engage healthy behaviours.

Answer 23

Selection bias