Repeatability or test–retest reliability is the closeness of the agreement between the results of successive

measurements Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared t ...

of the same

measure Measure may refer to: * Measurement, the assignment of a number to a characteristic of an object or event Law * Ballot measure, proposed legislation in the United States * Church of England Measure, legislation of the Church of England * Mea ...

, when carried out under the same conditions of measurement. In other words, the measurements are 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 In statistics, dispersion (also called variability, scatter, or spread) is the extent to which a distribution is stretched or squeezed. Common examples of measures of statistical dispersion are the variance, standard deviation, and interquart ...

and

inter-observer variability In statistics, inter-rater reliability (also called by various similar names, such as inter-rater agreement, inter-rater concordance, inter-observer reliability, inter-coder reliability, and so on) is the degree of agreement among independent obse ...

. A measurement may be said to be ''repeatable'' when this variation is smaller than a pre-determined acceptance criterion. Test–retest variability is practically used, for example, in

medical monitoring In medicine, monitoring is the observation of a disease, condition or one or several medical parameters over time. It can be performed by continuously measuring certain parameters by using a medical monitor (for example, by continuously measuri ...

of conditions. In these situations, there is often a predetermined "critical difference", and for differences in monitored values that are smaller than this critical difference, the possibility of variability as a sole cause of the difference may be considered in addition to, for example, changes in diseases or treatments.

Conditions

The following conditions need to be fulfilled in the establishment of repeatability: *the same experimental tools *the same observer *the same measuring instrument, used under the same conditions *the same location *repetition over a short period of time. *same objectives Repeatability methods were developed by Bland and Altman (1986). If the

correlation In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics ...

between separate administrations of the test is high (e.g. 0.7 or higher as in this Cronbach's alpha-internal consistency-table), then it has good test–retest reliability. The repeatability coefficient is a precision measure which represents the value below which the

absolute difference The absolute difference of two real numbers x and y is given by , x-y, , the absolute value of their difference. It describes the distance on the real line between the points corresponding to x and y. It is a special case of the Lp distance for ...

between two repeated test results may be expected to lie with a probability of 95%. The

standard deviation In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while ...

under repeatability conditions is part of

precision Precision, precise or precisely may refer to: Science, and technology, and mathematics Mathematics and computing (general) * Accuracy and precision, measurement deviation from true value and its scatter * Significant figures, the number of digit ...

and

accuracy Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements ( observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each oth ...

Attribute agreement analysis for defect databases

An attribute agreement analysis is designed to simultaneously evaluate the impact of repeatability and

reproducibility Reproducibility, also known as replicability and repeatability, is a major principle underpinning the scientific method. For the findings of a study to be reproducible means that results obtained by an experiment or an observational study or in a ...

on accuracy. It allows the analyst to examine the responses from multiple reviewers as they look at several scenarios multiple times. It produces statistics that evaluate the ability of the appraisers to agree with themselves (repeatability), with each other (

), and with a known master or correct value (overall accuracy) for each characteristic – over and over again.

Psychological testing

Because the same test is administered twice and every test is parallel with itself, differences between scores on the test and scores on the retest should be due solely to measurement error. This sort of argument is quite probably true for many physical measurements. However, this argument is often inappropriate for psychological measurement, because it is often impossible to consider the second administration of a test a parallel measure to the first. The second administration of a psychological test might yield systematically different scores than the first administration due to the following reasons: # The attribute that is being measured may change between the first test and the retest. For example, a reading test that is administered in September to a third grade class may yield different results when retaken in June. One would expect some change in children's reading ability over that span of time, a low test–retest correlation might reflect real changes in the attribute itself. # The experience of taking the test itself can change a person's true score. For example, completing an anxiety inventory could serve to increase a person's level of anxiety. #

Carryover effect The carryover effect is a term used in clinical chemistry to describe the transfer of unwanted material from one container or mixture to another. It describes the influence of one sample upon the following one. It may be from a specimen, or a reag ...

, particularly if the interval between test and retest is short. When retested, people may remember their original answer, which could affect answers on the second administration.

References

External links

Practical explanation of repeatability and reproducibility in terms of how data can be different between samples. - oil industry example
{{Webarchive, url=https://web.archive.org/web/20170922112516/http://learnoilanalysis.com/how-can-results-for-the-same-sample-be-different/ , date=2017-09-22 Statistical reliability Metrology ja:再現性

Conditions

Attribute agreement analysis for defect databases

Psychological testing

See also

References

External links