What is meant by validity? How does it differ from reliability and what are its types?

What is meant by validity? How does it differ from reliability and what are its types?
Answer-
Validity is a measurement scale, may be considered to be valid if it effectively measures a specific property or characteristic that it intends to measure.

Reliability and validity are closely interlinked. A measuring instrument that is valid is always reliable, but the reverse is not true. That is, an instrument that is reliable is not always valid. However, an instrument that is not valid may or may not be reliable and an instrument that is not reliable is never valid.

 

Validity may be classified into different types, as described below-

1)    Content validity: 

This type of validity may be of two types –

a) Face validity - Face validity is determined through a subjective evaluation of a measuring scale. For example, a researcher may develop a scale to measure consumer attitudes towards a brand and pre-test the scale among a few experts. If the experts are satisfied with the scale, the researcher may conclude that the scale has face validity. However, the limitation of this type of validity is that it is determined by opinions, rather than through a statistical method.

b) Sampling validity - Sampling validity refers to how representative the content of the measuring instrument is. In other words, the measuring instrument’s content must be representative of the content universe of the characteristic being measured.

2)    Predictive validity: 

 This type of validity refers to the extent to which one behavior can be predicted based on another, based on the association between the results yielded by the measuring instrument and the eventual outcome.

Example – In the case of an admission test designed for prospective MBA students, the predictive validity of the test would be determined by the association between the scores on the test and the grade point average secured by students during the first semester of study. A statistical measure of this association – the correlation coefficient – could be computed to determine the predictive validity of the admission test. Predictive validity would be strong if the coefficient is greater than .50..

3) Construct validity: 

A construct is a conceptual equation that is developed by the researcher based on theoretical reasoning. Various kinds of relationships may be perceived by the researcher between a variable under study and other variables. These relationships must be tested in order to determine the construct validity of a measuring instrument. The instrument may be considered to have construct validity only if the expected relationships are found to be true.

When determining the validity of a particular measurement instrument, all the three types of validity discussed above should be determined.