Table 1.

Definitions of terms often used with regard to immunization data

Term	Definition	References
Trueness (also “accuracy” and “unbiasedness”)	Closeness of a measurement or estimate to the exact or true value of the thing that was intended to be measured; (N.B.: ISO definition further specifies accuracy being combination of both “trueness” and precision)	[17, 23–25]
Concurrence (or “congruence”)	Degree of agreement between different methods intended to measure the same thing
Precision	Degree of spread of a series of observations or measurements - combination of repeatability and reproducibility; how tightly the distribution of an estimator clusters about its center; degree of being free of random error	[17, 24, 26]
Reliability (or “consistency”)	Repeated estimates/measurements produce similar results under similar conditions; the closeness of the initial estimated value(s) to the subsequent estimated values	[17, 24]
Repeatability	Degree of agreement (variation) of a measurement under constant conditions using the same instrument with the same operator over a relatively short period of time	[17]
Reproducibility	Degree of agreement (variation) of a measurement under non-standardized conditions, i.e., same measurement method but conducted by different operators over longer periods of time.	[17, 23]
Usability	Degree to which data are of sufficient quality (accuracy), completeness, timeliness to allow for effective decision making
Utilization (or “Use”)	Degree to which data are actually used in decision-making
Validity	Degree to which an assessment measures what it is intended to measure; degree of being free of systematic error	[17, 24, 27]