Reliability and Validity

Why Are They Important?

You will face many important decisions that will affect people’s lives if you become a professional psychologist. For example:

• Is this person clinically depressed?
• Does this child really have a learning disability?
• Is this treatment or drug really going to help this person?

You will want to choose measures and you will want to evaluate studies based upon whether or not they are reliable and valid. Your knowledge of these two concepts is one of the most important tools you’ll have.

Besides, if you are going to remain a psychology major, then believe me, you are going to hear about reliability and validity until the cows come home. So buckle in and resolve to get these two concepts down pat. They are two very different ideas, so make sure you can tell the difference between them.

First, understand this: psychologists measure things they believe exist in people's heads. Pretty crazy. Think about it:

• Have you ever seen a person's self-esteem?
• Can you get out a ruler and measure someone's intelligence?
• Are you extroverted? Then where exactly is your "extroversion" located? About three inches in from your right eye and then 1 inch over to the left?

Moral: psychologists measure things that we cannot see, but we believe them to exist inside your head. We had better be able to support that belief. To do it, we rely on reliability and validity. Let's take a look.

Reliability

What would you do with a bathroom scale that gave you a different weight every time you stood on it? You'd throw it out. In the same way, if you are going to have any faith in a psychological measure (like intelligence or extroversion), then you at least have to get the same score (or at least something close) each time you give the test to someone. That's reliability. You gotta have it or no one will believe that you know what you are talking about.

What about all the items on a standardized test that are supposed to measure some construct like mathematical ability? You would think that all the items would tend to agree with each other. I mean that one subset of items shouldn't say you stink in math while another subset says that you are great. This is another form of reliability. Ever take a survey over the phone and they seem to ask you the same question twice. They are checking to see if you are reliable.

Moral: When you think about reliability, think CONSISTENCY. If the psychological concept you are interested in really does exist inside people’s heads, then you should always find it when you look for it. If you do always find it, that is, if your subjects always respond consistently, then people will start to believe that you really have something there. Or in other words, your car should start each day and not catch fire.