Content validity
The first form of evidence relates to the content of the test.A comparison of test specification and test content is the basis for judgements as to content validity.But this in itself does not ensure content validity.We would not expect an achievement test for intermediate learners to contain iust the same set of structures as one for advanced learners.A test in which major areas identified in the specification are under-represented - or not represented at all - is unlikely to be accurate.A test is said to have content validity if its content constitutes a representative sample of the language skills, structures, etc.The test would have content validity only if it included a proper sample of the relevant structures.In order to judge whether or not a test has content validity, we need a specification of the skills or structures, etc.The best safeguard against this is to write full test specifications and to ensure that the test content is a fair reflection of these.But it will provide the test constructor with the basis for making a principled selection of elements for inclusion in the test.It is obvious that a grammar test, for instance, must be made up of items relating to the knowledge or control of grammar.