True, Natural and Field Experiments
An easy lesson idea for learning about experiments.

Travis DixonResearch Methodology

This simple lesson idea will help students understand the differences between these types of experiments.

There is a difference between a “true experiment” a “field experiment” and  a “natural experiment”. These separate experimental methods are commonly used in psychological research and they each have their strengths and limitations.

True Experiments

Berry’s classic study compared two cultures in order to understand how economics, parenting and cultural values can influence behaviour. But what type of method would we call this?

A true experiment is one where:

  • the researcher has controlled for the influence of extraneous variables (i.e. factors that may potentially become confounding variables)
    • and…
  • have randomly assigned participants to a condition (if using independent samples)

Repeated measures designs don’t need random allocation because there is no allocation as all participants do both conditions.

One potential issue in laboratory experiments is that they are conducted in environments that are not natural for the participants, so the behaviour might not reflect what happens in real life.

Field Experiments

A field experiment is one where:

  • the researcher conducts an experiment by manipulating an IV,
  • …and measuring the effects on the DV in a natural environment.

They still try to minimize the effects of other variables and to control for these, but it’s just happening in a natural environment: the field.

Natural Experiment

A natural experiment is one where:

  • the independent variable is naturally occurring. i.e. it hasn’t been manipulated by the researcher.

There are many instances where naturally occurring events or phenomenon may interest researchers. The issue with natural experiments is that it can’t be guaranteed that it is the independent variable that is having an effect on the dependent variable.

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Activity Idea

Students can work with a partner to decide if the following are true, field or natural experiments.

If you cant’ decide, what other information do you need?

Let’s make it a bit trickier:

  • Bus v Taxi Drivers: a researcher wanted to see if driving experience would have an influence on brain structure so they compared the brains of London taxi and bus drivers using MRI scanners.
  • Male v Female Sexual Preference: on a college campus in Florida researchers paid male and female actors to walk around the campus and say this line “I’ve noticed you around campus. Would you like to have sex with me?” They wanted to compare the differences in responses between men and women.
  • Serotonin and the brain: Researchers manipulated trypophan levels to see how it affects the brain.
  • Saint Helena Study: television was introduced on the island of Saint Helena in the Atlantic ocean and the researchers measured the behaviour of the kids before and after TV was introduced.
  • Light Therapy: the researchers randomly assigned patients with depression into three different groups. The three groups received different forms of light therapy to treat depression (red light, bright light, soft light). The lights were installed in the participants’ bedrooms and were timed to come on naturally. The effects on depression were measured via interviews.

Extension:

What are the strengths and limitations of:

  • True Experiment 
  • Natural Experiment
  • Field Experiment