Lecture 13: preventitive medicine 2 Flashcards
What is screening?
a public health service in which members of a defined population who do not necessarily perceive they are at risk of or already affected by a disease, are asked a question or offered a test to see who are more likely to be helped than harmed by further tests or treatment
What is sensitivity?
proportion of people with the disease who are identified as having a positive test result
What is specificity
the proportion of people without the disease who are correctly re-assured by a negative test result
What is the positive predictive value?
the probability that a person with a positive test result actually has the disease
What is the negative predictive value?
Probability that a person with a negative test result does not actually have the disease
What occurs with high sensitivity?
Maximise identification of diseased people in the screened population
relatively few false negatives
lots of flase positives- unnecessary investigations and treatment s
What occurs with high specificity?
Tend to detect only people with disease
relatively few false positives
may miss people who are at risk of the disease
lots of false negatives
When would high sensitivity be desirable?
Adverse consequences of missed diagnosis for individual or society
Diagnosis is to be confirmed by other tests so period of anxiety is short, or correct diagnosis is given before treatment is started
When would high specificity be desirable?
The diagnosis is associated with anxiety or stigma
further investigation are time consuming, expensive or painful
cares are likely to be detected by other means i.e. its too late for effective treatment
treatment is to be offered without further investigation
What is lead time bias?
early diagnosis falsely appears to prolong survival
In regards to principles and practice of screening for a disease: condition?
important health problem, detectable risk factor, disease marker
In regards to principles and practice of screening for a disease: Test?
Simple, safe etc. cut off level agreed, acceptable to population, agreed policy and further investigation
In regards to principles and practice of screening for a disease: Treatment?
effective, evidence, clinical management optimised before screening
In regards to principles and practice of screening for a disease: screening programme?
Evidence from RCTs that it reduces mortality/morbidity, socially/ethically acceptable, benefit should outweigh harm, cost effective, all other options considered
