Specificity and sensitivity Flashcards
what are these tests used for
to quantify the intrinsic ability of diagnostic tests to discriminate between people who have disease and people who do not have disease
what is a sensitive test
the proportion of people with the disease who will have a positive result
- a highly sensitive test is one that correctly identifies patients with the disease
a highly sensitive test will
identify all patients who have the disease
what is a a specific test
the proportion of people without the disease who will have a negative result. Refers to how well a test identifies patients who do not have the disease
a highly specific test
will identify 100% of patients who do not have the disease
positive predictive value
the probability of patients who have a positive test, actually having the test
e.g. you are tested for a type of cancer and the txt has a PPV of 15.2%. That means if your test comes back positive, you’d have a 15.2% chance of actually having cancer.
true positives
have the disease and correctly test positive
false negative
have the disease and incorrectly test negative
true negative
don’t have the disease and correctly test negative
false positive
don’t have the disease and incorrectly test positive
sensitivity is affected by
the severity or stage fl a disease- e.g. more advanced cancer is more likely to be picked up
specificity of a test is affected by
the extent to which those without the target disease ave symptoms that are commonly associated with diseased cases.
- presence of symptoms without disease reduce specificity
prevalence
the proportion of people with the disease
positive predictive and negative predictive values
predictive values quantify the likelihood that somebody has the disease based on their test result. determined by sensitivity and specificity, as well as prevalence
on the table: sensitivity
a/a+c
