Session 6 - Introduction to Screening

Question 1

What 4 criteria must a screening programme fulfil?

Answer 1

The disease/ condition
The test
The programme
The treatment

Question 2

Describe the disease/ condition criteria

Answer 2

Must have an early detectable stage
Epidemiology and pathological process must be well understood
Important health problem

Question 3

Describe the test criteria for a screening programme

Answer 3

The test must be simple and safe, precise and valid.
There also must be a cut off score to who to test further
Must be acceptable to the population

Question 4

Describe the treatment criteria for a screening programme

Answer 4

Must be based on evidence

Early treatment must be advantageous

Question 5

Describe the programme criteria for screening

Answer 5

Must have proven effectiveness 
Opportunity cost must be considered
Benefits outweigh potential physical and psychological harm 
Facilities for counciling   
Facilities for diagnosis and treatment 
Quality assurance

Question 6

Define screening

Answer 6

Systematic attempt to detect an unrecognisable conditions by use of examination, tests and procedures which a re rapid and cheap. Used to distinguish between we’ll people who may or may not have the disease in a defined population who are at risk/ already have disease

Question 7

What is sensitivity?

Answer 7

The proportion of people with the disease who test positive

a/a+c

Question 8

What is specificity?

Answer 8

The proportion of non cases that test negative = d/(b+d)

Question 9

What is positive predictive value?

Answer 9

The chance that if you test positive that you are actually a case of the disease
the more prevalent a disease is the higher the PPV will be
PPV = a/(a+b)

Question 10

Negative predictive value is the

Answer 10

chance of if I test negative what is the chance I don’t actually have the disease d/(c+d)

Question 11

What are some of the implications for false postives?

Answer 11

• Undergo unnecessary and often invasive procedures with their associated anxieties and risks
• Low uptake of screening processes in the future

Question 12

What are the implications for false negatives?

Answer 12

will go undiagnosed and not be offered tests which will benefit them
false reassurance

Question 13

What are the 6 main issues raised by screening?

Answer 13

1. Alteration of normal doctor patient contact
2. Complexity of screening programme
3. Evaluating the screening programme
4. Limitations of screening programme
5. Sociological critiques

Question 14

Describe the alteration of normal contact

Answer 14

Doctors are seeking out patients, targeting people who have not sought help and may not need it.
well people may suddenly become patients
need for evidence that screening may alter the progression of the disease

Question 15

How is screening complex?

Answer 15

Many results are true negatives so it is cost effective?

Questions over over treatment, the right population being screened and the anxiety/ psychological impact screening has

Question 16

Why is everyone not screened?

Answer 16

• Certain diseases are more likely to effect those of different ages
• Pathophysiology of disease differs at different stages
• Avoid unnecessary anxiety, treatment and investigations

Question 17

What is lead time bias?

Answer 17

• Early diagnosis falsely prolongs surivival
• Patients ‘appear to live longer’
• Reality is they have just be diagnosed early

Question 18

What is length time bias?

Answer 18

Screening normally targets slow growing, less aggressive cases. More likely favourable diagnosis of these diseases anyway. Also, these diseases may have never have causes a problem anyway.
Therefore, you may conclude that screening lengthens the lives of people found

Question 19

What is selection bias?

Answer 19

People who are screened are more likely to be the type of people who do other things to prevent disease….healthy volunteer effect.

Question 20

What are the limitations of screening?

Answer 20

• Screening may cause more harm than good (false reassurance, over treatment and psychological impact)
• Delivering informed choice is difficult

Question 21

What are the 5 sociological critiques of screening?

Answer 21

1. The nanny state - people have to present their bodies for inspection
2. Victim blaming - Individuals are encouraged to take responsibility for their own health
3. Opportunity costs (why not spend the money trying to address the underlying cause of disease?)
4. Screening is now seen as the sensible thing to do, deviance from this is seen to be irresponsible
5. Feminist agreement - women are screened more than man (not as much of an issue as it once was)