Screening Flashcards
What’s the purpose of screening?
Give a better outcome compared with finding something the usual way (having symptoms)
Finding something earlier is not the primary objective, a better prognosis is.
What’s the criteria of screening?
-condition: must be important health problem,where epidemiology and natural history understood, and all other cost-effective primary preventions implemented
-test: simple, safe, precise and validated
-intervention: evidence that intervention at present-symptomatic phase leads to better outcomes
-screening programme: proven effectiveness in decreasing mortality and benefit gained by individuals outweighs harms, cost-effective
-implementation: optimised in all healthcare providers and management/monitoring programme (quality assurance)
What is a false positive result?
An individual who doesn’t have the disease being screened for gets a positive result
What is a false negative result?
An individual who has the disease being screened for gets a negative result
Difficulties in evaluating screening?
-lead time bias: early diagnosis falsely prolongs survival, live same length, just know about disease for longer
-length time bias: screening better at picking up slow growing unaggressive than fast aggressive tumours. Shows better prognosis but not threatening, fast growing not counted in stats as aren’t picked up, false conclusion that screening lengthens lives of those found positive.
-selection bias: screening skewed by healthy volunteers. Need random controlled trial
What is sensitivity?
Proportion of people with the disease who test positive. High sensitivity= good at picking up the disease.
A / (a + c)
What is specificity?
Proportion of people without the disease who test negative. High specificity = good at ruling out people who do not have the disease.
B / (b+d)
What is positive predictive value?
Probability that someone who has tested positive actually have the disease.
A/ (a+b)
What is negative predictive value?
Proportion of pole who have tested negative who do not actually have the disease.
D / (c+d)
What factors affect screening uptake?
-acceptability of the test (non-invasive/invasive)
-awareness of benefits of screening (risks of morbidity/mortality)
-convenience
-accessibility (people with disabilities)
-reminders and endorsements
What’s the importance of informed choice?
-more holistic approach to evaluation
-respect for consumer autonomy in decision making
-lead to more benefit>harm
-assess effectiveness of particular screening programme
What are some difficulties in informed choice?
Communicating benefits/risks of preventive interventions can be challenging
