The concept of data reliability can be complicated and can take many forms. In general, reliability can be defined as how accurate the data is and the level of consistency of the collected data. In other words, the extent to which an experiment, test, or measuring procedure yields the same results on repeated trials is the measure of its reliability. For example, if one were to take a tape measure and find the length of a specific table, measuring the table repeatedly should yield the same result. If this is the case, then the data obtained are reliable.
Reliability can also be characterized as inter-rater (different people using the same measuring tape and measuring the same table multiple times) versus intra-rater (the same person measuring the same table several times, using the same measuring tape). There are statistical tests that can be run to identify the data’s reliability and consistency.