Reliability

Objectivity
Validity

Definition

The reliability of a measuring method 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 faulty, regardless of whether the test measures what it claims to measure. (This corresponds to the validity)

Deficiencies in reliability

The following deficiencies in the measurement can lead to a reduction in reliability.

Deficiencies in instrumental consistency
Defects in the constancy of characteristics
Deficiencies in the constancy of conditions

1. defects in instrumental consistency

Errors in instrumental consistency are those errors that either affect the instrument itself or any errors that result from incorrect operation of the instrument.

Error on the measuring device (measuring in the narrower sense, e.g. no calibration, error on lactate measuring devices, hand stop vs. electronic stop)
Errors in the operation of the device (measuring in a broader sense, e.g. incorrect operation of a stopwatch, errors in the evaluation)

2. defects in the constancy of characteristics

Defects in the constancy of characteristics occur particularly strongly when athletes/test persons do not achieve nearly the same result in repeated measurements. For example, if an athlete does several sprints over 10m., even if the external conditions remain the same, the same value is never measured. Question: Which time corresponds to the true value.

Note: The more demanding the task in terms of coordination, the higher the error in the consistency of the characteristics (example: free throws basketball vs. sprint performance). Also note: The higher the qualification of the athlete, the lower the error in the consistency of the characteristics. (Consistency of characteristics increases)

3. defects in the constancy of conditions

If external conditions change, this almost always leads to a falsification of the measurement results. One speaks thereby of a condition fluctuation (material-specific, milieu-specific, psychophysical) examples:

Leather vs. Rubber
Bounce on sprung floor vs. asphalt
Running on tartan or asphalt
Condition test at different temperature or wind conditions