| Definition | Justification of importance | |
| Reliability | Degree to which a measurement is consistent and free from error | Important to quantify error (systematic and random) so that true changes can be discerned from changes due to normal fluctuations |
| Validity | The gold standard outcome measures are often not feasible; therefore, it is important to know how an alternative outcome measure compares to the gold standard, and how different outcome measures compare It is important to know the ability of outcome measures to discriminate between different groups | |
| Concurrent validity | Degree to which a test correlates with a “gold standard” criterion test which has been established as a valid test of the attribute of interest | |
| Convergent validity | Degree to which a test correlates with another test which measures the same attribute | |
| Discriminate validity | Degree to which a test differentiates between groups of individuals known to differ in the attribute of interest | |
| Predictive validity | Degree to which an attribute can be predicted using the result of a predictor test/or degree to which prognosis can be predicted | |
| Responsiveness | Degree to which a test changes in response to an intervention known to alter the attribute of interest | Important attribute of tests used in clinical practice or research to assess treatment benefit (e.g. to identify improvements in response to an intervention) |
Reproduced from [1] with permission.