What is Internal Validity in Research? - Definition & Examples

What is Internal Validity in Research? - Definition & Examples
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  • 0:06 Internal Validity
  • 1:31 Importance
  • 2:43 Threats
  • 5:32 Lesson Summary
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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

The purpose of most research is to show that one variable causes changes in another variable. But, what happens when other variables come into play? In this lesson, we'll explore the definition, importance and threats to internal validity.

Internal Validity

Sean works for a large corporation, and they've hired someone to figure out if more money will mean more productivity for their workforce. In other words, they want to know if they pay Sean a higher salary, will he work more?

At first glance, the answer appears to be yes. After all, the people who get paid the most at the company tend to be the ones that come in early and stay late. They are the hardest working people in the company. So, it stands to reason that the more a person gets paid, the harder they will work, right?

Maybe, but it's actually a bit more complicated than that. Maybe those people get paid the most because they were already hard workers. Maybe they're motivated to work hard because they really like what they do and the pay is incidental. Maybe they are hyper competitive and don't want to be the first to leave the office.

How do we know what the cause of their hard work is? In research, internal validity is the extent to which you are able to say that no other variables except the one you're studying caused the result. For example, if we are studying the variable of pay and the result of hard work, we want to be able to say that no other reason (not personality, not motivation, not competition) causes the hard work. We want to say that pay and pay alone makes people like Sean work harder.

Importance

You may be wondering why we should care about internal validity. If people who work the hardest get paid the most, then why not just say that's what happens and call it a day?

The purpose of most research is to study how one thing (called the independent variable) affects another (called the dependent variable). The strongest statement in research is one of causality. That is, if we can say that the independent variable causes the dependent variable, we have made the strongest statement there is in research.

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