Repeatability
Encyclopedia
Repeatability or test-retest reliability is the variation
in measurement
s if they would have been taken by a single person or instrument
on the same item and under the same conditions. 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 some agreed limit.
Test-retest variability is practically used, for example, in medical monitoring 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 pre-test variability as a sole cause of the difference may be considered in addition to, for examples, changes in diseases or treatments.
Repeatability methods were developed by Bland and Altman (1986).
If the correlation
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
between two repeated test results may be expected to lie with a probability of 95%.
The standard deviation
under repeatability conditions is part of precision
and accuracy.
traits such as extraversion, which are believed to change only very slowly. In contrast, if you were trying to measure mood, you would expect only moderate test-retest reliability, since people's moods are expected to change from day to day. Very high test-retest reliability would be bad, since it would suggest that you were not picking up on these changes.
Variation
- Physics :* Magnetic variation, difference between magnetic north and true north, measured as an angle* Variation , any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon- Mathematics :* Bounded variation...
in measurement
Measurement
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...
s if they would have been taken by a single person or instrument
Measuring instrument
In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...
on the same item and under the same conditions. 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 some agreed limit.
Test-retest variability is practically used, for example, in medical monitoring 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 pre-test variability as a sole cause of the difference may be considered in addition to, for examples, changes in diseases or treatments.
Establishment
According to the Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, the following conditions needs to be fulfilled in the establishment of repeatability:- the same measurement procedure
- the same observer
- the same measuring instrument, used under the same conditions
- the same location
- repetition over a short period of time.
Repeatability methods were developed by Bland and Altman (1986).
If the correlation
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
between separate administrations of the test is high (e.g. 0.7 or higher as in this Cronbach's alpha-internal consistency-table
Internal consistency
In statistics and research, internal consistency is typically a measure based on the correlations between different items on the same test . It measures whether several items that propose to measure the same general construct produce similar scores...
),
then it has good test-retest reliability.
The repeatability coefficient is a precision measure which represents the value below which the absolute difference
Absolute difference
The absolute difference of two real numbers x, 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...
between two repeated test results may be expected to lie with a probability of 95%.
The standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
under repeatability conditions is part of precision
Accuracy and precision
In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...
and accuracy.
Desirability of repeatability
Test-retest reliability is desirable in measures of constructs that are not expected to change over time. For example, if you use a certain method to measure an adult's height, and then do the same again two years later, you would expect a very high correlation; if the results differed by a great deal, you would suspect that the measure was inaccurate. The same is true for personalityPersonality type
Personality type refers to the psychological classification of different types of individuals. Personality types are sometimes distinguished from personality traits, with the latter embodying a smaller grouping of behavioral tendencies. Types are sometimes said to involve qualitative differences...
traits such as extraversion, which are believed to change only very slowly. In contrast, if you were trying to measure mood, you would expect only moderate test-retest reliability, since people's moods are expected to change from day to day. Very high test-retest reliability would be bad, since it would suggest that you were not picking up on these changes.
See also
- Monitoring (medicine)Monitoring (medicine)In medicine, monitoring is the evaluation of a disease or condition over time.It can be performed by continuously measuring certain parameters , and/or by repeatedly performing medical tests .Transmitting data from a monitor to a distant...
- Accuracy
- Accuracy and precisionAccuracy and precisionIn the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...
- ReproducibilityReproducibilityReproducibility is the ability of an experiment or study to be accurately reproduced, or replicated, by someone else working independently...