Difference Between Validity and Reliability

The main difference between validity and reliability is that validity is the extent to which a test measures, and what it claims to measure whereas reliability refers to the consistency of the test results.

Tests or research of any kind is measured upon validity and reliability. Usually, these two measurements are used in psychological tests and research materials. Outside the research field, however, these two words are used interchangeably.

Key Areas Covered

1. What is Validity 
     – Definition, Features, Types
2. What is Reliability
     – Definition, Features, Types
3. What is the Relationship Between Validity and Reliability
     – Outline of Common Features
4. What is the Difference Between Validity and Reliability
     – Comparison of Key Differences

Key Terms

Reliability, Research, Validity

What is Validity?

Validity is the extent to which a test measures what it claims to measure. In other words, it means the accuracy of a test. Therefore, it is a scientific test or piece of research that actually measures what it sets out to measure, or how well it reflects the reality it claims to represent. 

Kelly (1927) who stated that a test is valid if it measures what it claims to measure, formulated the concept of validity. Thus, validity refers to the credibility or believability of the research. Say, for example, your test intends to measure the attitudes of a community towards a social practice of the area. So, if the test measures the attitude levels of the community regarding the particular social practice, without measuring anything else like the impact of the social practice on the social community, then we can say that the test is valid or the validity of the test is achieved. Therefore, validity is an indication of how sound your research or the test is.

There are two types of validity:

• Internal validity – the instruments or procedures used in the research study measured what they were supposed to measure
• External validity -If the results can be generalized beyond the immediate study

Both these types of validity are relevant to evaluating the validity of a research study or a procedure.

What is Reliability

Reliability refers to the degree to which the result of a measurement, calculation, or specification can be depended on to be accurate or the consistency of the test results. Therefore, we can claim that a test is reliable if the test results it produces is consistent without changing every time.

Hence, in brief, reliability is the parameter we can use to measure the stability or the consistency of the test from its test results. So if we take the same example we took before, if the test result is the same even when we do another time, using the same test subjects, then we can say that the test is reliable, or that the reliability of the test is achieved.

Similarly, if the results of a research study are replicated consistently, then the results or the finding of the test are reliable. Moreover, a correlation coefficient can be used to assess the degree of reliability. Thus, the theory is that if a test is reliable, it should show a high positive correlation.

There are two types of reliability we use when assessing reliability in a test. They are

• internal reliability – the extent to which a measure is consistent within itself
• external reliability – the extent to which a measure varies from one use to another

Relationship Between Validity and Reliability

• Validity and reliability are inter-related aspects in research. In other words, if the research or a test is valid, then the data is reliable. Yet, if a test is reliable, that does not mean that it is valid.

Difference Between Validity and Reliability

Definition

Validity refers to the extent to which a test measures, and what it claims to measure. Reliability, on the other hand, refers to the consistency of the test results.

Measurement

While validity measures whether the extent to which the test claims to measure is achieved, reliability measures whether the test gives consistent results at its outcome.

Types

There are two types of validity as internal validity and external validity whereas reliability has two types as internal and external reliability.

Conclusion

Validity and reliability are parameters of research and tests. Hence, for research to be of use, both these aspects should be there. The difference between validity and reliability is that validity refers to the extent to which a test measures, and what it claims to measure whereas reliability refers to the consistency of the test results. However, when the research or a test is valid, then the data is reliable. Yet, if a test is reliable, that does not mean that the test it is valid.

Reference:

1. McLeod, Saul. “Saul McLeod.” Simply Psychology, Simply Psychology, 1 Jan. 1970, Available here.
2. “Introduction: Reliability and Validity.” Content Analysis: Introduction, Available here.
3. McLeod, Saul. “Saul McLeod.” Simply Psychology, Simply Psychology, 1 Jan. 1970, Available here.

Image Courtesy:

1. “Knowledge, Discover, research” (CC0) via Public Domain Pictures