Nature of reliability

1. Reliability refers to the results obtained with an evaluation instrument and not to the instrument itself. 
2. Reliability refers to a type of consistency.
3. Reliability is a necessary but not a sufficient condition for validity.
4. Reliability merely provides the consistency that makes validity possible.
5- Reliability is a property of the assessment results rather than the property of the instrument.
6- It is more appropriate to speak of the reliability of assessment scores rather than the reliability of an assessment.
7- Reliability refers to the results (scores) of a test; not the test itself.
8- An estimate of reliability refers to a particular type of consistency.
·         Consistency over time. or,
·         Consistency among raters. or,
·         Consistency of performance across tasks.
·         Must have reliability to have validity.
9- A test can measure the same attribute with perfect consistency and not be valid.
10- Reliability is primarily statistical.
When estimating reliability, we are trying to determine how much measurement error is present; the less error, the more reliable the instrument.