Validity

Meaning of validity

• Validity refers to the degree to which a test measures what it claims to measure.
• Anastasi (1968:99) has defined validity as , "The validity of a test concerns what the test measures and how well it does so."
• Lindquist (1951:213) has defined validity of a test as "the accuracy with which it measures that which is intended to measure or as the degree to which it approaches infallibility in measuring what it purports to measure."
• Kaplan and Saccuzzo (2001) have defined validity as "the agreement between a test score or measure and the quantity it is believed to measure.“

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Meaning of validity

• While reliability is referred to as the ‘self correlation’ of the test, validity is the correlation with some outside, independent criteria which measures what the test is meant to measure.
• ‘Independent criteria’ refer to some measure of the traitor the group of traits (outside the test) that the test itself claims to measure.
• For determining the validity of a test, the test must be compared with some ideal independent measures or criteria. The correlation coefficient computed between the test and the ideal measures or criteria is known as the validity coefficient.
• Validity is i,mportant for the generalizability of the test results.

Properties of validity

1. Validity is a relative term-

A test is not generally valid. It is valid only for a particular purpose. Thus, one validates not a measuring instrument, rather some uses to which the test is put.

2. Validity is not a fixed property of the test-

Validation is not a fixed process, rather an unending process. With the discovery of new concepts, and the formulation of new meanings the old contents of the test become less meaningful.

3. Validity, like reliability, is a matter of degree and not an all-or-none property-

A test meant for measuring a particular trait or ability cannot be said to be either perfectly valid or not valid at all.

Types of validity

There are mainly three types of validity:

• Content validity
• Criterion validity
• Construct validity

Content validity

• Content validity is also designated by other terms such as intrinsic validity, relevance, curricular validity and representativeness.
• Each individual item or content of the test should correctly and adequately sample or measure the trait or the variable in question and the test, as a whole, should contain only the representative items of the variable to be measured by the test.
• Anastasi (1968:100) has said that content validity, "involves essentially the systematic examination of the test content to determine whether it covers a representative sample of the behaviour domain to be measured."
• Content validity is needed in the tests which are constructed to measure how well the examinee has mastered the specific skills or a certain course of study.

Content validity

Content validity requires both item validity and sampling validity.

• Item validity is basically concerned with whether the test items represent measurement in the intended content area,
• Sampling validity is concerned with the extent to which the test samples the total content area

Content validity of a test is examined in two ways:

(i) by the expert's judgement

(ii) by statistical analysis (internal consistency, corelating two independent tests of the same factor, discrimination power of test)

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Content validity

The following points should be fully covered for ensuring full content validation of a test:

1. The area of content (or items) should be specified explicitly so that all major portions in equal proportion be adequately covered by the items. 2. Before the item writing starts, the content area should be fully defined in clear words

3. The relevance of contents or items should be established in the light of the examinee's responses to those contents and not in the light of apparent relevance of the contents themselves.

Face validity

• Face validity refers not to what the test actually claims to measure but to what it appears to measure superficially.
• Face validity is the mere appearance that the test has validity (Kaplan & Sacuzzo, 2001).
• When a test item looks valid to the group of examinees, the test is said to have face validity.
• The purpose of face validity is to establish rapport and secure co-operation because when test items do not appear to be valid to the examinees, they may not co-operate in responding and may give irrelevant answers because such items themselves appear to be irrelevant.

Criterion validity

CRITERION-RELATED VALIDITY

Criterion-related validity is one which is obtained by comparing (or correlating) the test scores with scores obtained on a criterion available at present or to be available in the future.

The criterion is defined as an external and independent measure of essentially the same variable that the test claims to measure.

Cureton (1965)- the validity of a test is an estimate of the correlation coefficient between the test scores and the "true" (that is, perfectly reliable) criterion scores.

There are two subtypes of criterion-related validity:

(a) predictive validity, and

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Criterion validity

• Predictive validity
• Predictive validity is also designated as empirical validity or statistical validity.
• In predictive validity a test is correlated against the criterion to be made available sometime in the future.
• Marshall & Hales (1972:110) have said, "The predictive validity coefficient is a Pearson product-moment correlation between the scores on the test and an appropriate criterion, where the criterion measure is obtained after the desired lapse of time."
• Predictive validity is needed for tests which include long-range forecast of academic achievement, forecast of vocational success and forecast of reaction to therapy.

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• Concurrent validity
• The test is correlated with a criterion which is available at the present time.
• Concurrent validity is most suitable to tests meant for diagnosis of the present status rather than for prediction of future outcomes.
• Concurrent validity can be determined by:
• Relationship method involves determination of the relationship between scores on the test and scores on some other established criterion which are concurrently available.
• The discrimination method of computing concurrent validity involves determining whether the test scores can be used to discriminate between people who posses different quantities of the trait being measured.

Construct validity

• An investigator decides to compute construct validity only when he is fully satisfied that neither any valid and reliable criterion is available to him nor any universe of content entirely satisfactory and adequate to define the quality of the test.
• Construct validity has also been given other names such as factorial validity and trait validity.
• Anastasi (1968:114) has defined it as "the extent to which the test may be said to measure a theoretical construct or trait."
• A construct is a non-observable trait, such as intelligence, which explains our behaviour.
• According to Nunnally (1970), a construct indicates a hypothesis which tells us that "a variety of behaviours will correlate with one another in studies of individual differences and/or will be similarly affected by experimental treatments.”

Construct validity

The process of validation involves the following steps:

• 1. Specifying the possible different measures of the construct
• 2. Determining the extent of correlation between all or some of those measures of construct
• 3. Determining whether or not all or some measures act as if they were measuring the construct

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Convergent & Divergent validity

• For a satisfactory construct validity it is essential that the test correlates with other theoretical measures with which it should correlate and it is equally essential that it must not correlate with other measures with which it should not.
• When the test correlates with its expected referents, the process is known as convergent validity
• When a test correlates poorly (or not at all) with measures with which it should not, because it differs from those referents or measures, the procedure is called discriminant validation. In this sense, the low correlation sometimes becomes the evidence for the validity of the test.

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Factors affecting validity

• Length of the Test
• Range of Ability (or Sample Heterogeneity)
• Ambiguous Directions
• Socio-cultural Differences
• Addition of Inappropriate Items