What is an “experiment?”

Travis DixonResearch Methodology

If you’re reading this it’s probably because your teacher has assigned this as homework because you’ve called a study an “experiment” when it wasn’t an experiment at all. So this post is to help you know exactly when to use the term “experiment”, and when it’s safe just to say “study.”

But before we get to that, let’s first clarify why this is important knowledge. I think there are two reasons:

  1. If you use the term experiment incorrectly in an exam it will suggest to the examiner that you have limited knowledge – this will affect your marks.
  2. Research methods (and especially experiments) are the backbone of psychological research and so they’re a pretty important concept to understand.

Definition of experiment:

An experiment in psychology is when there is a study conducted that investigates the direct effect of an independent variable on a dependent variable. 

Tip: If you’re not sure if it’s an experiment, you’re always safe to call it a “study.”

Before you can call a study an experiment, you have to identify the independent variable. Ask yourself:

  • “Are there different groups in the study that the researchers are comparing?”

For example, in this study about serotonin’s effects on the brain we can see that there are two groups: drinking the placebo or the drink that reduces serotonin. So the IV is serotonin levels.

Experiments test causal relationships. 

If there are different groups and there is clearly an IV, you then need to ask yourself, “are the researchers studying the effects on a DV?” In other words, is there a causal relationship between the IV and DV being examined?

If you look at the examples in the studies in this post, you’ll see that all of these studies are clearly investigating the effects of an IV on a DV:

  • Serotonin study: the effects of serotonin levels (IV) on prefrontal cortex activity (DV)
  • Rat experiment: the effects of testosterone (IV) on aggression (DV)
  • Watching TV (Bandura): the effects of observing violence (IV) on aggression (DV).

So if the study is testing a causal relationship between an IV and a DV, you my friend, have got yourself an experiment 🙂


Laboratories are good places to conduct experiments because the conditions can be controlled so the IV can be isolated – this is essential when testing causal relationships.

So when is a study not an experiment?

A simple test would be to ask yourself:

  • Did the researchers create the groups/conditions?

If they did, then you’ve got an experiment.

  • Serotonin study: the researchers chose who drank which drink and when.
  • Rat study: the researchers chose which rats to castrate and which ones not to.
  • TV study: they told which kids to watch TV and which ones not to.

If the researchers didn’t create the groups you might be better to call it a “study” to be on the safe side.

In a true experiment it is the researchers who manipulate the independent variable (i.e. they create the groups/conditions in the experiment).

For example, in studies that compare cultures the researchers cannot create the groups because people are born into their existing cultures. These types of studies are most commonly correlational studies.

Another example is research on communication in relationships: the researchers compare the differences between couples with positive communication with those who have negative communication, but they didn’t create these groups – they occurred naturally. These are also correlational studies.

To conclude: if the researchers create the groups for comparison it’s an experiment. If not, you’re safer to call it a “study.”

Qualitative studies are never experiments, so be extra-careful when using this word in Paper 3.

But just to get tricky, there are some experiments where the independent variable is naturally occurring. These are called natural experiments (or quasi-experiments). So if you have a study with a naturally occurring variable, before you can call it an experiment you have to ask yourself:

  • Are they testing a causal relationship between the IV and the DV?

But the problem is in order to answer this question you need to know quite a bit about the methodology. This is because you have to know if they’ve controlled for confounding variables in either their design or their statistical analyses. If they’ve tried to control confounding variables and isolate the IV as the only variable affecting the DV, you can call it an experiment.

But here we’re getting pretty complicated, which is why it might better to err on the side of caution with naturally occurring IVs and call them studies if you’re not sure if they’re experimental or not (another way to check is to ask your teacher).

What makes an experiment “quasi?” (Read More)

I hope this post helps. If you need anything clarified or you have questions about a specific study, please feel free to post it in the comments.