# What is the relationship between reliability and validity?

The relationship between reliability and validity is that they are both essential for any study or research project. Without them, the results will not be fit for purpose.

## Expert Answers

As the previous educators have pointed out, reliability is all about getting consistent results from a study. In contrast, validity is the extent to which your study actually does what it sets out to do.

In terms of a relationship, what is interesting to note about reliability and validity is that they are not mutually exclusive. In other words, you can have a study which is reliable but not valid and, equally, you can have a study that is valid but lacks reliability.

There are ways to boost both validity and reliability. For example, if I am designing an assessment for my history students, I would want an assessment that tests exactly what I have taught in previous lessons. Every student should be given the same amount of revision time and the same set of instructions on how to complete the test, including how long they have to complete the test. When it comes to marking the tests, I will need to use the same mark scheme for every student. This will give me high reliability and high validity.

However, this relationship is further complicated by the fact that there are different types of validity and reliability, and all of these various measures need to be carefully considered when designing an experiment or study. Please see the reference link for more information on these.

For any researcher, then, the goal is to have a study that is both high in validity and high in reliability because this will provide a set of high-quality results from which to draw conclusions and make an analysis.

Further Reading

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Reliability and validity are two sides of the coin of accurate measurements. In order to be perfectly accurate with a measurement or assessment, you need both reliability and validity. Although they may seem initially similar, they are both unique.

Reliability is akin to consistency. When you are measuring something, the frequency with which you receive similar results (in regards to the testing and test subjects being used) is reliability. If you measure the weight of a pig three times, and the weight is 300 the first time, 301 pounds the second, and 298 pounds the final time, that is relatively reliable. If however you received weights of 300, 382, and 207, those would not be reliable.

Validity is how close to the actual result your measurement puts you. If you know ahead of time that the cow weights 360 pounds, regardless of how consistently you receive 300 pounds approximately, you will know the system is not valid.

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In science and research, there are two different measures for how correct your testing is. One of these measures is validity, or precision, while the other is called reliability, or accuracy. Validity is how close to the correct result your measurement is (for instance, if you’re measuring how well a new thermometer tests temperature, and it registers water boiling at 211 degrees, that’s fairly valid compared to if it read 198 degrees). Reliability is a measure of how frequently you get the same result. You can be reliable without being valid, and vice versa.

Imagine a dartboard, for example. A valid result is getting close to the bullseye. A reliable result is consistently hitting the same value, even if it’s nowhere near a bullseye. For testing, you want your measurement system to be valid and reliable.

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Reliability is the ability of a test to yield the same findings or results each time it is conducted. A test that yields different results every time it is conducted with everything else being constant cannot be said to be a reliable test or study. Thus, reliability speaks to the consistency of the test or study, which means no variations in the observed results or findings.

Validity is the credibility of the study or the genuineness of the study. Results of a test should be correct by ensuring that what is being measured and the tools used to measure are what is required. Additionally, validity also refers to the ability of the results to be generalized to the study population. Thus, the results should apply to the same subjects beyond the study.

The relationship between the two is that if the study is valid, then it must be reliable. However, a study's reliability does not automatically attest to the validity of the study. Although necessary, reliability is not in itself a condition for validity.

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Validity is whether or not you are measuring what you are supposed to be measuring, and reliability is whether or not your results are consistent.

If an instrument or experiment is valid, it will usually also be reliable as long as it is carefully constructed to control all variables except the one being studied.

“For a test to be valid, or truthful, it must first be reliable.” (educational assessment)

For example, if you are measuring the reading levels of students after a new computer-based reading program has been used, you will want to make sure that your test will get the same results every time it is taken, and it should if it accurately measures the students’ reading ability.

If an instrument or experiment is reliable, it does not necessarily have to be valid.  You might get consistent results, but not actually be measuring what you think you are measuring.  For example, if the above test of reading level was really a vocabulary test, you might get the same results each time but the results do not show reading level.

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