In statistics and psychometrics,<unk> is the overall consistency of a measure. A measure is said to have a high<unk> if it produces similar results under consistent conditions:"It is the characteristic of a set of test scores that relates to the amount of random error from the measurement process that might be embedded in the scores. Scores that are highly reliable are precise, reproducible, and consistent from one testing occasion to another. That is, if the testing process were repeated with a group of test takers, essentially the same results would be obtained. Various kinds of<unk> coefficients, with values ranging between 0.00 (much error) and 1.00 (no error), are usually used to indicate the amount of error in the scores." For example, measurements of people's height and weight are often extremely reliable.
Reliability 
Data validation
Inter-rater reliability
Construct validity
Proportional reporting ratio
Appropriate use criteria
Relative biological effectiveness
Indicative limit value