Validity

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What is Validity? :)
Question: What is Validity?

Answer: Validity is the extent to which a test measures what it claims to measure. It is vital for a test to be valid in order for the results to be accurately applied and interpreted.

Validity isn’t determined by a single statistic, but by a body of research that demonstrates the relationship between the test and the behavior it is intended to measure. There are three types of validity:

Content validity:
When a test has content validity, the items on the test represent the entire range of possible items the test should cover. Individual test questions may be drawn from a large pool of items that cover a broad range of topics.

In some instances where a test measures a trait that is difficult to define, an expert judge may rate each item’s relevance. Because each judge is basing their rating on opinion, two independent judges rate the test separately. Items that are rated as strongly relevant by both judges will be included in the final test.

Criterion-related Validity:
A test is said to have criterion-related validity when the test is demonstrated to be effective in predicting criterion or indicators of a construct. There are two different types of criterion validity:
* Concurrent Validity occurs when the criterion measures are obtained at the same time as the test scores. This indicates the extent to which the test scores accurately estimate an individual’s current state with regards to the criterion. For example, on a test that measures levels of depression, the test would be said to have concurrent validity if it measured the current levels of depression experienced by the test taker.
* Predictive Validity occurs when the criterion measures are obtained at a time after the test. Examples of test with predictive validity are career or aptitude tests, which are helpful in determining who is likely to succeed or fail in certain subjects or occupations.

Construct Validity:
A test has construct validity if it demonstrates an association between the test scores and the prediction of a theoretical trait. Intelligence tests are one example of measurement instruments that should have construct validity.
By Kendra Van Wagner
http://psychology.about.com/mbiopage.htm

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Added by. Pamenan Mato Nan Hilang
How to know good construct validity
Prior to this issue, Ensure that you have known about construct validity. There are three most widely accepted forms of validity are (Hair et al, 2006, p-137):
1. Convergent validity - assesses the degree to which two measures of the same
concept are correlated. Here the researcher may look
for alternative measures of a concept and then correlate
them with the summated scale. High correlations here indi
cate that the scale is measuring its intended concept.
Criteria: factor loading>0,4; or >0,5-0,6; or >0,7

2. Discriminant validity - is the degree to which two conceptually similar
concepts are disticnt. The empirical test is again
the correlation among measures, but this time the
summated scale is correlated with a similar, but
conceptually distinct measure. Now the correlation
should be low, demonstrating that the summated scale is
sufficiently different from the other similar concept
Criteria: not redundancy in factor loading; AVE; Cross loading.

3. Nomological Validity- refers to the degree that summated scale makes accurate
predictions of the other concepts in a theoritically
based model. The researcher must identify theoritically
supported relationship from prior research or accepted
principles and then assess wheter the scale has
corresponding relationship.
In summary, convergent validity confirms that the scale is correlated with other known measures of the concept; discriminant validity ensure that the scale is sufficiently different from other similar concepts to be distinct; and nomological validity determines wheter the scale demonstrates the relationships shown to exist based on theory or prior research.