Validity is often seen as a close companion of reliability. Validity is the assessment of the evidence that indicates that an instrument is measuring what it claims to measure. An instrument can be highly reliable (consistent in measuring something) yet lack validity. For example, an instrument may reliably measure motivation but not valid in measuring income. The problem is that an instrument that measures motivation would not measure income appropriately.

In general, there are several ways to measure validity, which includes the following.

• Content validity
• Response process validity
• Criterion-related evidence of validity
• Consequence testing validity
• Face validity

Content Validity

Content validity is perhaps the easiest way to assess validity. In this approach, the instrument is given to several experts who assess the appropriateness or validity of the instrument. Based on their feedback, a determination of the validity is determined.

Response Process Validity

In this approach, the respondents to an instrument are interviewed to see if they considered the instrument to be valid. Another approach is to compare the responses of different respondents for the same items on the instrument. High validity is determined by the consistency of the responses among the respondents.

Criterion-Related Evidence of Validity

This form of validity involves measuring the same variable with two different instruments. The instrument can be administered over time (predictive validity) or simultaneously (concurrent validity). The results are then analyzed by finding the correlation between the two instruments. The stronger the correlation implies the stronger validity of both instruments.

Consequence Testing Validity

This form of validity looks at what happened to the environment after an instrument was administered. An example of this would be improved learning due to test. Since the the students are studying harder it can be inferred that this is due to the test they just experienced.

Face Validity

Face validity is the perception that the students have that a test measures what it is supposed to measure. This form of validity cannot be tested empirically. However, it should not be ignored. Students may dislike assessment but they know if a test is testing what the teacher tried to teach them.

Conclusion 

Validity plays an important role in the development of instruments in quantitative research. Which form of validity to use to assess the instrument depends on the researcher and the context that he or she is facing.