How the Experimental Method Works in Psychology

Female college student conducting scientific experiment in science laboratory classroom
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How exactly do researchers investigate the human mind and behavior? While there are a number of different research techniques, the experimental method allows researchers to look at cause-and-effect relationships.

In the experimental method, researchers identify and define key variables, formulate a hypothesis, manipulate the variables and collect data on the results. Extraneous variables are carefully controlled to minimize a potential impact on the outcome of the experiment.

Experimental Method in Psychology

The experimental method involves manipulating one variable to determine if changes in one variable cause changes in another variable. This method relies on controlled methods, random assignment and the manipulation of variables to test a hypothesis.

Types of Experiments

There are a few different types of experiments that researchers might choose to use. The type of experiment chosen might depend on a variety of factors including the participants, the hypothesis and the resources available to the researchers.

Lab Experiments

Lab experiments are very common in psychology because they allow experimenters more control over the variables. These experiments can also be easier for other researchers to replicate. The problem, of course, is that what takes place in a lab is not always identical to what takes place in the real world.

Field Experiments

Sometimes researchers might opt to conduct their experiments in the field. For example, let's imagine that a social psychologist is interested in researching prosocial behavior. The experimenter might have a person pretend to faint and observe to see how long it takes onlookers to respond.

This type of experiment can be a great way to see behavior in action in realistic settings. However, it makes it more difficult for the researchers to control the variables and can introduce confounding variables that might influence the results.


While lab experiments represent what are known as true experiments, researchers can also utilize a type known as a quasi-experiment. Field experiments can be either quasi-experiments or true experiments.

Quasi-experiments are often referred to as natural experiments because the researchers do not have true control over the independent variable.

Instead, the treatment level is determined by the natural conditions of the situation. A researcher looking at personality differences and birth order, for example, is not able to manipulate the independent variable in the situation. Treatment levels cannot be randomly assigned because the participants naturally fall into pre-existing groups based on their birth order in their families.

So why would a researcher choose to use a quasi-experiment? This is a good choice in situations where scientists and interested in studying phenomena in natural, real-world settings. It is also a good choice in situations where researchers cannot ethically manipulate the independent variable in question.

Key Terms to Know

In order to understand how the experimental method works, there are some key terms you should first understand.

The independent variable is the treatment that the experimenter manipulates. This variable is assumed to cause some type of effect on another variable. If a researcher was investigating how sleep influences test scores, the amount of sleep an individual gets would be the independent variable.

The dependent variable is the effect that the experimenter is measuring. In our previous example, the test scores would be the dependent variable.

Operational definitions are necessary in order to perform an experiment. When we say something is an independent variable or dependent variable, we need to have a very clear and specific definition of the meaning and scope of that variable.

A hypothesis is a tentative statement or guesses about the possible relationship between two or more variables. In our earlier example, the researcher might hypothesize that people who get more sleep will perform better on a math test the next day. The purpose of the experiment is then to either support or fail to support this hypothesis.

The Experimental Process

Psychologists, like other scientists, utilize the scientific method when conducting an experiment. The scientific method is a set of procedures and principles that guide how scientists develop research questions, collect data and come to conclusions.

The four basic steps of the process are:

  1. Forming a Hypothesis
  2. Designing a Study and Collecting Data
  3. Analyzing the Data and Reaching Conclusions
  4. Sharing the Findings

Most psychology students will be expected to use the experimental method at some point. If you want to take a closer look at the process, be sure to check out a step-by-step breakdown of how to conduct a psychology experiment for more information.

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  1. Radder H. The philosophy of scientific experimentation: a reviewAutom Exp. 2009;1:2. doi:10.1186/1759-4499-1-2