VALIDITY AND RELIABILITY
Validity refers to whether or not a test measures accurately what it is intended to measure.
We create language tests in order to measure such essentially theoretical constructs as ‘reading ability’, ‘fluency in speaking’, ‘control of grammar’, and so on.
There are different kinds of validity:
Construct Validity: It refers to the theory underlying the target; in recent years this term has been increasingly used to refer to the general, overarching notion of validity
Content Validity: 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.
For instance, a grammar test must be made up of items relating to the knowledge of grammar. It will have content validity only if it includes a proper sample of the relevant structures.
Criterion-Related Validity: Relates to the degree to which results on the test agree with those provided by some independent and highly dependable assessment of the candidate’s ability.
There are essentially two kinds of criterion-related validity: concurrent validity and predictive validity
Concurrent Validity is established when the test and the criterion are administered at about the same time. It usually uses statistical methods of correlation the other measures.
Predictive Validity concerns the degree to which a test can predict candidates’ future performance. For this type of validity, the correlation that is computed is based on the test results and the examinee’s later performance. It is especially useful for test purposes such as selections or admissions.
Reliability measures how well a test or assessment assesses what it claims to. It is the extent of which one test or assessment produces the same results if it were taken by the same pupils on different occasions, or if the same test or assessment were scored by different people
Reliability is important because test must be constructed, administered and scores in a way in which they can be administered in two different occasions to the same group of students and the results are similar
The concepts of validity and reliability are used to describe the technical quality of assessment practices. They are more often applied to testing, although are also important in alternative assessment.
Validity and reliability can be conflicting needs for assessment techniques and procedures. The most reliable assessments will be pencil and paper tests in which each item measures only a single aspect of a skill and which give each tester a numerical mark. But the most valid assessments will be on those that collect a lot of information about performance on several aspects of a skill. When validity increased, reliability decreased.
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