Validity and Reliability: How to Assess the Quality of a Research Study

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  • 1:25 Reliability
  • 3:04 Validity
  • 3:14 Internal Validity
  • 4:23 External Validity
  • 5:37 Ecological Validity
  • 6:17 Lesson Summary
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Lesson Transcript
Instructor: Wind Goodfriend
Many psychologists and teachers complete research studies. How can you tell if a study was done well? This lesson will cover many criteria for a good quality study, including types of reliability and validity.

Introduction

Imagine you're an elementary school teacher, and you want to study whether you can predict how well children will learn spelling by assessing their personalities. You could complete this study in several different ways. Let's say that you give students a questionnaire that is supposed to measure a variety of different personality traits. Then you give the students a spelling test. How do you know if the study was done well or if it was of good quality?

This lesson will discuss ways that you can assess the quality of any research study, including studies that you read in professional journals, studies you hear about in the newspaper or studies that you design yourself.

This lesson covers the concepts of reliability and validity. In a different lesson, you'll also learn about reliability and validity, but it will be in a different context. Psychologists discuss reliability and validity when they talk about whether assessments are of good quality, such as whether a certain intelligence test really measures intelligence. Assessment in school is also relevant to reliability and validity, but there are different types of reliability and validity for assessments and for research studies. This lesson focuses on research studies only.

Reliability

The first criterion for whether a study is done well is called reliability. Reliability is a measure of the consistency of scores over time. There are different types of reliability in terms of research studies.

The first type of research reliability is whether the results are reliable across time; that is, if the same researcher would get the same results if he or she did the same study at a different time. Let's go back to the example of a teacher who tests whether personality predicts spelling ability. If that teacher does the study in one year and gets certain results, the teacher would want to do the exact same study the next year and the year after that to see if the results are stable across time. If they are, then the teacher can be much more confident in making conclusions. If the results are not reliable across time, then the teacher should be more cautious in making any conclusions.

A second type of reliability would be if a different teacher wanted to try doing the same study. Imagine the first teacher calls a friend in a different school and tells that friend about the results. Then, the second teacher does the same study on a different set of children in a different school. If both teachers get the same results, then we can say that the results are reliable across samples or across groups of people who are participating in the study. We could also say that the results are reliable across experimenters.

All of these types of reliability are important so researchers can be confident in saying that results are true across time and across different settings.

Validity

Besides reliability, validity is also important in research studies. Just like with reliability, there are different kinds of validity within a research study.

The first type of validity is called internal validity. Within an experiment, you are usually making conclusions about some kind of cause and effect relationship, such as concluding that personality affects spelling ability. So, internal validity is defined as making sure that the cause-effect relationship identified in the study is really there, and there are no other explanations for the results.

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