| Biostatistical Term | Abbreviation | Definition |
|---|---|---|
| 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+ PV- |
Percentage of patients with a positive or negative test for a disease who do or do not have the disease in question. |
| Pretest probability |
Probability of disease before a test is performed. | |
| Post-test probability |
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. |