Screening test statistics Flashcards
what is sensitivity ?
Proportion of patients with the condition who have a positive test result
how do we calculate sensitivity ?
TP (test positive - disease present ) / TP + FN (test negative with disease present) )
what is specificity ?
Proportion of patients without the condition who have a negative test result
how to we calculate specificity ?
TN ( Test negative -disease absent ) / TN + FP ( test positive with disease absent )
what is positive predictive value ?
chance that the patient has the condition if the diagnostic test is positive
how to calculate positive predictive value ?
TP (test positive with disease present ) / TP + FP (tested positive and disease absent )
what is negative predictive value ?
chance that the patient has the condition if the diagnostic test is negative
how do recalculate negative predictive value
TN (Tested negative with disease absent ) / TN - FN
what is Likelihood ratio for a positive test result?
How much the odds of the disease increase when a test is positive
how to calculate the Likelihood ratio for a positive test result?
sensitivity / (1 - specificity)
what is Likelihood ratio for a negative test result
How much the odds of the disease decrease when a test is negative
how to calculate Likelihood ratio for a negative test result?
(1 - sensitivity) / specificity
Positive and negative predictive values are
prevalence dependent
what is not prevalence dependant ?
Likelihood ratios are not
what os precision ?
ability to produce the same measurements with repeated tests.
