True experimental studies aim to establish cause and effect through the manipulation of an independent variable. They require a control group, experimental group(s), random assignment, and a researcher-manipulated variable. The control group receives no treatment while the experimental group receives the treatment. Outcomes are then compared between groups. There are three main true experimental designs: post-test only, pre-test post-test, and Solomon four-group, which combines elements of the first two designs to reduce errors. An example true experiment tests whether Drug X reduces anxiety levels through random assignment of participants to control and experimental groups receiving different doses or a placebo.

1. True Experimental Study
Design
Prepared by:
Prayas Gautam
Email:prayas.gautam007@gmail.com

2. Introduction
• A true experiment is a type of experimental design and is thought to
be the most accurate type of experimental research.
• 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

3. Criteria that must be met in a true
experiment
• Control group and experimental group
• Researcher-manipulated variable
• Randomization

4. 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 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.

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

6. Randomization
• Each research participant must have an equal chance of being
assigned to each sample group.
• Research participants have to be randomly assigned to either the
control or experimental group.

7. Example of true experimental study
• Hypothesis : Drug X causes decrease in anxiety level.
• Independent Variable = Drug X ( Dose can be manipulated)
• Dependent Variable = Anxiety level
Sample population 600 (people with anxiety)
200
Control Group
(Placebo)
200
Experimental Group 2
250 mg dose of X daily
200
Experimental Group 1
100 mg dose of X daily
Randomization
Cure 10
No cure 190
Within 3 months
Cure 90
No cure 110
With in 3 months
Cure 190
No cure 10
Within 3 months
Comparison

8. Types of True experimental study
• Post test only design
• Pre-test- Post-test design
• Solomon four group design

9. Post test only design
• This type of design has two randomly assigned groups: an
experimental group and a control group.
• Neither group is pretested before the implementation of the
treatment. The treatment is applied to the experimental group and
the post-test is carried out on both groups to assess the effect of the
treatment or manipulation.
• This type of design is common when it is not possible to pre-test the
subjects.

10. R X O1
R O2
R = Randomization
O1 = Post test in experimental
X = Intervention
O2 = Post test in control

11. Pre-test- Post-test design
• The subjects are again randomly assigned to either the experimental
or the control group.
• Both groups are pretested for the independent variable.
• The experimental group receives the treatment and both groups are
post-tested to examine the effects of manipulating the independent
variable on the dependent variable.

12. R O1 X O2
R O3 O4
R = Randomization
O1 = Pre test in experimental
X = Intervention
O2 = Post test in experimental
O3 = Pre test in control
O4 = Post test in control

13. Solomon four group design
• Subjects are randomly assigned into one of four groups.
• There are two experimental groups and two control groups. Only two
groups are pretested.
• One pretested group and one unprotested group receive the treatment.
• All four groups will receive the post-test.
• The effects of the dependent variable originally observed are then
compared to the effects of the independent variable on the dependent
variable as seen in the post-test results.
• This method is really a combination of the previous two methods and is
used to eliminate potential sources of error.

14. References
• http://study.com/academy/lesson/true-experiment-definition-
examples.html
• https://cirt.gcu.edu/research/developmentresources/research_ready
/experimental/design_types
• A text book of epidemiology ; Rajesh Karki, Rajan Poudel