Confidence interval
Range between two values within which it is probable that the true value lies for the whole population of patients from which the study patients were selected.

Sensitivity
The proportion of people with a positive test result among those with the target condition. See also Sensitivity analysis;

Sensitivity analysis
Any test of the stability of the conclusions of a health care evaluation over a range of probability estimates, value judgments, and assumptions about the structure of the decisions to be made. This may involve the repeated evaluation of a decision model in which one or more of the parameters of interest are varied.

P value
The probability that results as extreme as or more extreme than those observed would occur if the null hypothesis were true and the experiment were repeated over and over. A P value <0.05 means that there is a less than 1 in 20 probability that, on repeated performance of the experiment, the results as extreme as or more extreme than those observed would occur if the null hypothesis were true.

Probability
Quantitative estimate of the likelihood of a condition existing (as in diagnosis) or of subsequent events (such as in an intervention study).

Number needed to harm
The number of patients who, if they received the experimental intervention, would lead to one additional patient being harmed over a specific period of time. It is the inverse of the absolute risk increase (ARI), expressed as a percentage (100/ARI).

Number needed to screen
The number of patients who would need to be screened to prevent one adverse event.

Number needed to treat
The number of patients who need to be treated over a specific period of time to achieve one additional good outcome. When discussing NNT, it is important to specify the intervention, its duration, and the desirable outcome. It is the inverse of the absolute risk reduction (ARR), expressed as a percentage (100/ARR).

Absolute risk reduction
The absolute difference (risk difference) in risks of harmful outcomes between experimental groups (experimental group risk, or EGR) and control groups (control group risk, or CGR), calculated as the risk of harmful outcome in the control group minus the risk of harmful outcome in the experimental group (CGR – EGR). Typically used to describe a beneficial exposure or intervention (eg, if 20% of patients in the control group have an adverse event, as do 10% among treated patients, the ARR or risk difference would be 10% expressed as a percentage or 0.10 expressed as a proportion).

Predictive value
Two categories: Positive predictive value—the proportion of people with a positive test result who have the disease; negative predictive value—the proportion of people with a negative test result and who are free of disease.

G Mohan.