Repeatability or
test–retest reliability is the in
measurements taken by a single person or
instrument on the same item, under the same conditions, and in a short period of time. A less-than-perfect test–retest reliability causes
test–retest variability. Such variability can be caused by, for example,
intra-individual variability and
intra-observer variability. A measurement may be said to be
repeatable when this variation is smaller than a pre-determined acceptance criteria.