Test characteristics Flashcards
Definition of ‘Sensitivity of the test’
Proportion of those with a disease which it correctly identifies
Formula for sensitivity
True positives/ True positives+false negatives
Definition of ‘specificity’
Proportion of those without the disease which it correctly identifies
Formula for specificity
True negatives/true negatives+false positives
Definition of positive predictive value
Probability that a subject has the disease given that they have a positive result
Formula for positive predictive value
True positives/ true positives+false positives
Definition of negative predictive value
Probability that subject doesn’t have disease given they have a negative result
Formula for negative predictive value
True negatives/ true negatives/false negatives
Formula for PPV
(sensitivity x prevalence)/ sensitivity x prevalence +((1-specificity)x (1-prevalence))
Whats a diagnostic test
Confirm or exclude prevalence of disease
Whats a screening test
Assess risk of disease to determine need for confirming diagnostic test
Whats a prognostic test
Assess risk of future disease and need for preventative measures
Difference between screening and diagnostic tests
screening- large no. of people. Simple + acceptable and high sensitivity
Diagnostic-expensive and invasive
Whats the Bayes test
Likelihood ration of a test: likelihood that a positive test would be accepted in a patient with the disease compared to the likelihood in a patient without
What are the past dest odds equL TO
Pre test odds
