True Experiment: Definition & Examples

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  • 0:01 Definition & Criteria…
  • 2:58 Example of a True Experiment
  • 5:27 Another Example of a…
  • 6:43 Lesson Summay
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Lesson Transcript
Instructor: Yolanda Williams

Yolanda has taught college Psychology and Ethics, and has a doctorate of philosophy in counselor education and supervision.

A true experiment is thought to be the most accurate experimental research design. Learn more about true experiments from examples and test your knowledge with a quiz.

Definition and Criteria of a True Experiment

Sarah is a researcher at a children's psychiatric center. Her office has just been asked to conduct a pilot study on a new prescription medication used to treat anxiety called Drug X. Sarah wants to figure out if Drug X causes a reduction in anxiety like the drug company claims. How can Sarah answer this question? One method would be to conduct a true experiment.

A true experiment is a type of experimental design and is thought to be the most accurate type of experimental research. This is because a true experiment supports or refutes a hypothesis using statistical analysis. A true experiment is also thought to be the only experimental design that can establish cause and effect relationships. So, what makes a true experiment?

There are three criteria that must be met in a true experiment

  1. Control group and experimental group
  2. Researcher-manipulated variable
  3. Random assignment

Let's look at each of these requirements more closely.

Control Group and Experimental Group

True experiments must have a control group, which is a group of research participants that resemble the experimental group but do not receive the experimental treatment. The control group provides a reliable baseline data to which you can compare the experimental results. The experimental group is the group of research participants who receive the experimental treatment. True experiments must have at least one control group and one experimental group, though it is possible to have more than one experimental group.

Researcher-Manipulated Variable

In true experiments, the researcher has to change or manipulate the variable that is hypothesized to affect the outcome variable that is being studied. The variable that the researcher has control over is called the independent variable. The independent variable is also called the predictor variable because it is the presumed cause of the differences in the outcome variable.

The outcome or effect that the research is studying is called the dependent variable. The dependent variable is also called the outcome variable because it is the outcome that the research is studying. The researcher does not manipulate the dependent variable.

Random Assignment

Research participants have to be randomly assigned to the sample groups. In other words, each research participant must have an equal chance of being assigned to each sample group. Random assignment is useful in that it assures that the differences in the groups are due to chance. Research participants have to be randomly assigned to either the control or experimental group.

Let us go back to Sarah's example to show what a true experiment looks like.

Example of a True Experiment

Sarah has come up with a hypothesis, or educated guess, as to what the relationship between Drug X and anxiety are. Sarah's hypothesis is that Drug X causes a decrease in anxiety. Sarah's independent, or predictor, variable is Drug X. Her dependent, or outcome, variable is anxiety. Sarah will manipulate the dose of Drug X to see if it causes a decrease in anxiety.

Sarah collects a random sample of 600 individuals who have completed a baseline assessment and were found to have high levels of anxiety. She divides them into three groups.

The first group is a control group, which will receive a sugar pill each day as a placebo. A placebo is a substance that looks like a medication or some other treatment, but has no therapeutic effect. The sugar pill looks like Drug X so that the control group will think that they are being treated. This helps control for the placebo effect, which is when participants improve just because they believe that they are receiving a treatment. If the anxiety level of the individuals in the control group improves just as much or more than the anxiety levels of the experimental groups, we can say that there is a placebo effect and the reduction in anxiety is not caused by Drug X.

The second group is the low-dose experimental group. The participants in the second group receive 100 mg of Drug X each day.

The third group is the high-dose experimental group. The participants in the third group receive 250 mg of Drug X each day. Each of the 600 participants has an equal chance of being assigned to any of the three groups.

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