Population Based Screening Flashcards
How would you define screening?
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
How would you define a diangosis?
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
What are the purposes of screening?
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
What are some of the populaiton screening programmes currently taking place in the UK?
Bowel cancer
Breast cancer
Cervical screening
Diabetic eye screening
What are the critera for a condition to be sutiable to create a screening programme for it?
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
What are some of the features of the test that should be involved in a screening programme?
Simple, safe, precise and valid, and disturbution of the test values in a population must be known and a agreeded cut off point reached
What is a false postive?
When you refer a well person for further investigation
What is a false negative?
When you fail to refer a person who already has an early form of the disease
What are the main features of test valdity?
Sensitivity, specificity, positive predictive value, and negative predictive value
What is the senstivity of a test?
The proportion of people with the condition that test positive, can be calculated as true positives/ (true positives + false negatives)
What is the speficity of a test?
The proportion of people without the disease who are test negative, can be calculated by true negatives / (false postives + true negatives)
What are some of the key features of the sensitivity and specificty of tests?
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
What is the postive predictive value?
If a person is test postive, how likley they are to have the disease and is calculated by true postives/ (true postives + false psotives)
Which factors of test populations are affected by the prevenalnce of a test within a population?
The positive predictive value and the negative predicitve value
What is the negative predictive value?
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)
What are some of the possible implications of false postive results?
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
What are some of the implications of false negative results?
They will not be offered the diangostic testing they needs, and this gives false reassurance meaning that they may actually present later with symptoms
What are some of the features of the ideal screening intervention?
Effective, with evidence that intervention at the presymptomatic phase leads to better outcomes for the screened indidual
What are some of the ideal features of the screening programme?
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
What is a lead time bias?
Early diagnosis appears to prolong survival,as patients live the same length of time but longer knowing that they have the disease
What is a length time bias?
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
What is the selection bias evaluation difficulty of screening programmes?
Skewed by the healthy volunteer effect, as those who have regualr screening are more likley to do other things that protect them from disease.
What are the main sociological critques of screening?
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
