The reliability (reliability) of a measurement process is defined as the degree of accuracy with which a feature is measured. A feature is considered reliable if the determined value is only slightly error-prone, regardless of whether the test measures what it claims to be measuring. (This corresponds to the validity)
The following measurement defects can lead to Decrease in reliability to lead.
Under errors in the instrumental consistency are understood to mean those errors that either affect the measuring device itself or any errors that arise from incorrect operation of the device.
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Defects in the Feature constancy occur particularly strongly when athletes / test persons do not achieve approximately the same result when repeating measurements.
E.g. for several sprints over 10m. of an athlete, even with constant external conditions, the same value is never always measured. Question: What time corresponds to the true value.
Notice: The more demanding the task in terms of coordination, the higher the error in the constancy of features (Example free throws basketball vs. sprint performance)
Note further: The higher the qualification of the athlete, the lower the deficiencies in the constancy of characteristics. (Constancy of characteristics increases)
If external conditions change, this almost always leads to a falsification of the measurement results. One speaks of one Condition fluctuation (material-specific, milieu-specific, psychophysical)
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In order to be able to work with sufficiently reliable data, the following values are recommended for practice. The measurement error is then still in the acceptable range.
The following methods are used in practice to determine reliability:
A test and that Retest is carried out at different times under identical conditions. A change of the experimenter enables simultaneous determination of objectivity and reliability.
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Two different tests with the same goal (identical scope) are carried out on the same sample. (Parallel test reliability)
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Note: Not all tests can be regarded as parallel tests.
The requirement for the Test halving method is that the test can be broken into two equivalent halves. (Ex. 20 free throws from the free throw line in basketball).
In some tests, halving is not possible (e.g. squats)
Action:
Both test halves are summed up and correlated with one another.
Options for halving the test:
In the Consistency analysis the test is broken down into the number of parts as there are tasks. The measure of the internal consistency is that Alpha coefficient to Cronbach.