Reliability and Validity in Language Assessment

Both reliability and validity are important for a language test to be useful.

Reliability

Reliability in other words is consistency. It is like a weighing scale's reliability. A weighing scale must show the same weight of the same object on all occasions. If a test that gives me an A grade today must give me something similar a month from now also. Or a test that gives A grades to a group of students of the same ability must give about the same scores in a few weeks' time. That is, the test must be reliable. If a test gives A grade today, and F (fail) grade tomorrow, then the test is not reliable. If tests are not reliable, they are not useful. They will not provide us with any information about the test-taker. Therefore, our attempts must be to minimize the effects of the potential sources of inconsistency in the test.

Validity

Validity implies the meaningfulness and appropriateness of the interpretations we make based on a test score. Validity is when we are indeed testing what we intend to test. Validity is when we are confidently able to interpret the test score as a representation of the test-taker's underlying language ability we measured in the test. If there is no validity, we cannot generalize our interpretations to the Target Language Use (TLU) domain. If we can't generalize a test score to other domains, it is not very useful. In other words, without validity, tests are useless.

To ensure validity, we must look at the characteristics of the test task and the construct definition. Test task characteristics are important because they must match with the TLU domain tasks' characteristics. They must test the test-takers' language ability. This is possible only when you have defined the construct to be measured in clear terms.