Lakhasly

Content validity
The first form of evidence relates to the content of the test. A test is said to have content validity if its content constitutes a representative sample of the language skills, structures, etc. with which it is meant to be concerned. It is obvious that a grammar test, for instance, must be made up of items relating to the knowledge or control of grammar. But this in itself does not ensure content validity. The test would have content validity only if it included a proper sample of the relevant structures. lust what are the relevant structures will depend, of course, upon the purpose of the test. We would not expect an achievement test for intermediate learners to contain iust the same set of structures as one for advanced learners. In order to judge whether or not a test has content validity, we need a specification of the skills or structures, etc. that it is meant to cover. Such a specification should be made at a very early stage in test construction. It isn't to be expected that everything in the specification will always appear in the test; there may simply be too many things for all of them to appear in a single test. But it will provide the test constructor with the basis for making a principled selection of elements for inclusion in the test. A comparison of test specification and test content is the basis for judgements as to content validity. Ideally these judgements should be made by people who are familiar with language teaching and testing but who are not directly concerned with the production of the test in question.
What is the importance of content validity? First, the greater a test's content validity, the more likely it is to be an accurate measure of what it is supposed to measure, i.e. to have construct validity. A test in which major areas identified in the specification are under-represented - or not represented at all - is unlikely to be accurate. Secondly, such a test is likely to have a harmful backwash effect. Areas that are not tested are likely to become areas ignored in teaching and learning. Too often the content of tests is determined by what is easy to test rather than what is important to test. The best safeguard against this is to write full test specifications and to ensure that the test content is a fair reflection of these. For this reason, content validation should be carried out while a test is being developed; it should not wait until the test is already being used.