Population Based Screening

Question 1

How would you define screening?

Answer 1

A systematic attempt to detect an unrecognised condition by the application of tests examinations or other procedures, and these can be applied rapidly or cheaply to distinguish between an apparently well person who probably has a disease and those who probably do not

Question 2

How would you define a diangosis?

Answer 2

The definintive identification of a suspected disssease or defect by the application of tests, examinations and other procesdures, which can be extensive to definitively label people as having a disease or not having a disease

Question 3

What are the purposes of screening?

Answer 3

To give a better outcome compared to finding a condition in the usual way, if treatment can wait until symptoms present then there is no point screening for a condition

Question 4

What are some of the populaiton screening programmes currently taking place in the UK?

Answer 4

Bowel cancer
Breast cancer
Cervical screening
Diabetic eye screening

Question 5

What are the critera for a condition to be sutiable to create a screening programme for it?

Answer 5

Should be an important health problem, with epdiemology, incidence and prevelance and natural history understood
Cost effective primary prevention should have been implemented
If the carriers of a mutation are identified, the natural history of this mutation should be well understood

Question 6

What are some of the features of the test that should be involved in a screening programme?

Answer 6

Simple, safe, precise and valid, and disturbution of the test values in a population must be known and a agreeded cut off point reached

Question 7

What is a false postive?

Answer 7

When you refer a well person for further investigation

Question 8

What is a false negative?

Answer 8

When you fail to refer a person who already has an early form of the disease

Question 9

What are the main features of test valdity?

Answer 9

Sensitivity, specificity, positive predictive value, and negative predictive value

Question 10

What is the senstivity of a test?

Answer 10

The proportion of people with the condition that test positive, can be calculated as true positives/ (true positives + false negatives)

Question 11

What is the speficity of a test?

Answer 11

The proportion of people without the disease who are test negative, can be calculated by true negatives / (false postives + true negatives)

Question 12

What are some of the key features of the sensitivity and specificty of tests?

Answer 12

They are functions of the characteristics of the test, and when the same test is applied in the same way in a different population they will remain the same

Question 13

What is the postive predictive value?

Answer 13

If a person is test postive, how likley they are to have the disease and is calculated by true postives/ (true postives + false psotives)

Question 14

Which factors of test populations are affected by the prevenalnce of a test within a population?

Answer 14

The positive predictive value and the negative predicitve value

Question 15

What is the negative predictive value?

Answer 15

The proportion of people who are test negative and actually do not have the disease, can be calculated by true negatives/ (false negatives + true negatives)

Question 16

What are some of the possible implications of false postive results?

Answer 16

They will be refferred to possibly invasive diagnostic testing, turned into patients when not actually ill, and may lead to anxiety and real cost and oppurtunity cost, and also may lead to a lower uptake of screening programmes

Question 17

What are some of the implications of false negative results?

Answer 17

They will not be offered the diangostic testing they needs, and this gives false reassurance meaning that they may actually present later with symptoms

Question 18

What are some of the features of the ideal screening intervention?

Answer 18

Effective, with evidence that intervention at the presymptomatic phase leads to better outcomes for the screened indidual

Question 19

What are some of the ideal features of the screening programme?

Answer 19

Proven effectiveness in reducing mortailty and morbidity, there should be evidence that is socially acceptable, and any benefit should be greater than the consequences of false negative and false positive results

Question 20

What is a lead time bias?

Answer 20

Early diagnosis appears to prolong survival,as patients live the same length of time but longer knowing that they have the disease

Question 21

What is a length time bias?

Answer 21

Screening programmes are better at picking up slow growing causes then fast growing aggressive ones, and therefore the diseases that are detectable through screening are more likely to have a favourable outcome, and may never have caused a problem. Can lead the false conclusion that screening is useful in length ing lives

Question 22

What is the selection bias evaluation difficulty of screening programmes?

Answer 22

Skewed by the healthy volunteer effect, as those who have regualr screening are more likley to do other things that protect them from disease.

Question 23

What are the main sociological critques of screening?

Answer 23

Victim blaming and indidualsing pathology- and pulling away from some of the more sociological causes
Surveillance on the public
Moral obligation- those who choose not to screen are seen as ignorant or morally deviant
Feminist critiques- showing women’s bodies as unruly and out of contro