Other bits Flashcards
Define screening
presumptive identification of unrecognised disease
using a test or procedure which can be applied rapidy
to sort out apparently well persons who propbably have a disease from those who probably do not
What are the principles of a good screening programme when it comes to the disease
known aetiology and risk factors
known natural history
high incidence/.prevalence
high morbidity/mortality
What are the principles of a good screening programme when it comes to the test
simple
acceptable
valid
reliable
What are the principles of a good screening programme when it comes to the treatment
available
effective
acceptable
benefits from early detrtection
What are the principles of a good screening programme when it comes to the programme
cost-effective
agreed protocol
quality assurance
does more good than harm
Define sensetivity
people with the disease having an abnormal result
/ all people with disease
Define specificity
people without disease having normal test result
/ all people without disease
define positive predicitve value
people with disease who had abnormal test result
/ all people who tested positive
how likely an abnormal test result is going to be right
define negative predictive value
people without disease with normal test result
/ all people with normal test result
What affects the PPV and NPV
the specificity and sensitivity
the prevalence - high prevalence = high PPV and low NPV
What are the consequences of a high PPV
many people would have an abnormal test result
anxiety and stress
unnecessary investigations
to then find out they are fine!
What are the consequences of a low NPV
many people with abnormal result assume they are fine
delay seeking medical advice
when they might have the disease!
What is lead-time bias
screening brings forward time of diagnosis, so it looks as if survival time has increased.
infact, the time of diagnosis has just been changed, still die at same time!
What is length bias
selective detection of less aggressive cancers by a screening programme which would have better prognosis anyway
aggressive cancers grow more rapidly, so there is less of a chance for a screening test o detect them
survival results are better for those detected by screening, but this would have been the case anyway due to the cancer being less aggressive!
