Free tool · Biostatistics
Likelihood Ratio Calculator
Enter a test's sensitivity and specificity to get LR+ and LR−, with interpretation.
LR+ (positive test)
6.00
Moderate increase in disease probability
LR− (negative test)
0.12
Moderate decrease in disease probability
What a likelihood ratio tells you
A likelihood ratio tells you how much a test result should shift your estimate of disease probability. LR+ (positive test) and LR− (negative test) are properties of the test itself — unlike predictive values, they don't change with disease prevalence, which is what makes them useful for applying a test's performance to a specific patient's pretest probability.
The formulas
LR+ = sensitivity / (1 − specificity) — how much more likely a positive result is in someone with the disease versus without.LR− = (1 − sensitivity) / specificity — how much less likely a negative result is in someone with the disease versus without.
Using it: pretest to posttest probability
A likelihood ratio is most useful combined with a pretest probability to get a posttest probability — see the pretest/posttest probability calculator to take the LR from here and apply it.