Difference Between Validity vs Reliability

If a thing is correct today, it does not really mean it will be correct tomorrow or the next day. This can be said of our wristwatch or wall clock, which brands are popular, customer behavior, and so on. We will expand on this matter from a basic point of view with regards to accuracy and consistency. In the course of this informative post, we will go ahead to discuss the basic difference between reliability and validity after we begin with their definitions below.

Definition of Validity

Validity is defined as the yardstick that shows the degree of accuracy of a process or the correctness of a concept. Accuracy may vary depending on how well the results correspond with established theories. There are 3 different types of validity.

• Criterion

This type is all about the performance of a measuring instrument with the aim of showing if the instrument provides accurate and expected results or estimates. It can also be said to be the extent to which a procedure is related to an outcome in a situation. If an employee performs brilliantly at the job after taking and passing a performance test, then the test can be classified as having criterion validity.

• Content

This is a way of determining the extent to which a test covers a particular subject. A very good example is a school setting where students are given a class test on a particular subject. The purpose of this test is to evaluate the students’ understanding of the test topic.

• Construct

This is a way of measuring the accuracy of a test to demonstrate that it is actually doing what it is intended for. This is not related to how the test is designed or what test is being given. Rather, it deals with how a person responds to the test as a result of their emotions, proficiency, skills, etc.

Generally, it is usually not easy to determine the validity of a specific answer because it can be debated.

Definition of Reliability

Reliability is defined as how often a test score is correct when a particular tool or procedure is employed. To determine what is the difference between reliability and validity, you can state that in the case of reliability, the emphasis lies on the keyword “consistency,” while in the other case, the emphasis lies on the keyword “accuracy.”

When a measuring tool, for instance, provides the very same result when subjected to a specific condition, then that tool can be said to be consistent. To really assess the consistency of a process, one would usually conduct an evaluation through methods such as test-retest, alternative forms, and internal consistencies.

Another way of illustrating the difference between validity and reliability is by defining the types of reliability, what they stand for, and some examples to back them up.

• Interrater

This has to do with the variations in the results of different people observing the same event. In this case, the event is a constant that does not change. It has to be tested by a number of different observers. The degree of difference in the results of their observation is what is referred to as interrater reliability.

The America’s Got Talent TV show is a very good example of interrater reliability. A contestant comes on stage to sing, for instance; then the judges observe and rate the contestant based on their respective opinions. If the results from the judges are the same, then the interrater consistency is high. Otherwise, it is low.

• Test-retest

Just like the name implies, you have to test a thing and then retest it again as many times as possible. The idea behind this type of test is to determine the level of consistency of a process with the aim of finding out if the results would change or remain the same over time.

Here is an example. A group of students takes an exam designed to reveal their knowledge about a particular subject. If they repeat the same exam after some time, say months, and they give the exact same answers as the first time, it shows a high test-retest reliability rate.

• Internal consistency

This involves testing a particular construct (or event) from different points of view without repetition or involving others in it. It can also mean assessing the correlation between multiple items on a test. With this test, you can evaluate the internal consistency of questions by the answers supplied. For example, a customer questionnaire asking for simple yes or no answers could be judged for internal consistency reliability.

Main Differences Between Validity vs Reliability

Now, let us show in a tabular form the difference between validity and reliability. This will further simplify the meanings and applications of these terms.

Basis of Comparison	Validity	Reliability
Meaning	The yardstick that shows the degree of accuracy of a procedure	How often a test score is correct when a particular tool or procedure is employed
Deals with	Accuracy	Consistency
Instrument	An accurate instrument can be relied on	A consistent instrument may not always be accurate
Relatable question	Does it quantify what it is supposed to quantify?	Does it produce the same result after multiple tests?
Ease of procedure	Involves detailed analyses, which can be challenging to resolve	Does not involve a lot of analysis and is easier
Dependency	Cannot exist without the other	Can exist without the other
Examples	– Construct – Criterion – Content – Internal	– Interrater – Test-retest – Internal

Difference Between Validity and Reliability: Conclusion

As far as comparison is concerned, reliability vs validity will always be considered. A procedure or an instrument may be accurate, but if it is not consistent with its accuracy, then it cannot be relied on. This means that a measuring instrument (for instance) can be accurate but not dependable.

The accuracy of a procedure or a measuring instrument involves quite a number of detailed analyses, which can be challenging at times. This is not the case with consistency. It does not involve a lot of analysis and is easy to resolve.