|Sensitivity||Sn||Percentage of patients with disease who have a positive test for the disease in question.|
|Specificity||Sp||Percentage of patients without disease who have a negative test for the disease in question.|
|Predictive value (positive and negative)||PV+
|Percentage of patients with a positive or negative test for a disease who do or do not have the disease in question.|
|Probability of disease before a test is performed.|
|Probability of disease after a test is performed.|
|Likelihood ratio||LR||LR >1 indicates an increased likelihood of disease.
LR <1 indicates a decreased likelihood of disease.
The most helpful tests generally have a ratio of less than 0.2 or greater than 5.
|Relative risk reduction||RRR||The percentage difference in risk or outcomes between treatment and control groups. Example: if mortality is 30% in controls and 20% with treatment, RRR is (30-20)/30 = 33 percent.|
|Absolute risk reduction||ARR||The arithmetic difference in risk or outcomes between treatment and control groups. Example: if mortality is 30% in controls and 20% with treatment, ARR is 30-20=10%.|
|Number needed to treat||NNT||The number of patients who need to receive an intervention instead of the alternative in order for one additional patient to benefit. The NNT is calculated as: 1/ARR. Example: if the ARR is 4%, the NNT = 1/4% = 1/0.04 = 25.|
|95% confidence interval||95% CI||An estimate of certainty. It is 95% certain that the true value lies within the given range. A narrow CI is good. A CI that spans 1.0 calls into question the validity of the result.|