Reliability and Validity
To make statements that you can have confidence in means establishing validity. There are several kinds. Let's do a quick review of three common types of validity: Internal, External and Construct.
- Internal Validity: When you think about internal validity, think INSIDE the experiment. Is your experiment so well designed that when the results are in, you feel confident that you can make truthful and definite statements about what happened in your study? If your study is relatively free of confounds; you will have high confidence in its results. That's internal validity.
- External Validity: When you think about internal validity, think OUTSIDE the experiment. Can your results be generalized to people outside of your study? Whether this is high or low depends on what you are studying and what your subjects are like. Just consider it carefully: will people not in your study react the same way as those in your study?
- Construct Validity: Think CONCEPT. You are manipulating and measuring many concepts in your study – are you really tapping into these concepts? Here's an example:
- Independent Variable: Suppose you wanted to study the effects of violent TV on aggression in children. Your first step is to decide which TV shows contain "violence". Whatever show you pick, you should first make sure that children perceive what THEY SEE in the show as violence. Is there a difference between cartoon violence and violence that involves real people? You have to think these issues through to make sure that you are truly (validly) manipulating the concept (or "construct" - really the same term) of a violent TV show.
- Dependent Variable: Suppose you decide (as early researchers did) to measure the "number of times a child hits a bobo doll" as your dependent measure of aggression (a bobo doll is that inflatable doll that bounces back up when you hit it). Now ask yourself: when a child hits a bobo doll, is this because of aggressive tendencies? If the answer is no (because hitting a bobo doll is simply a way of playing with it), then the number of hits on the doll would not accurately measure the construct of "aggression". You want to measure something that truly reflects the construct (concept) that you think is an expression of what is inside people's heads.
Here’s a graphic to help you organize and remember these important ideas:
Bottom Line:
- Reliability and validity are very easy conceptually but they strike to the heart of Psychology as a useful discipline.
