Experimental Design: Concept of Independent & Dependent variables

Independent and dependent variables are two fundamental concepts in experimental design. They help researchers understand the relationship between different factors in an experiment.

Independent Variable

The independent variable is the variable that the experimenter manipulates or changes. It is the presumed cause of the effect that is being measured in the experiment. For example, in an experiment to investigate the effect of fertilizer on plant growth, the amount of fertilizer applied would be the independent variable.

Dependent Variable

The dependent variable is the variable that is measured or observed in an experiment. It is the presumed effect of the independent variable. In the plant growth experiment, the height of the plants would be the dependent variable.

Relationship between Independent and Dependent Variables

The independent variable is thought to cause changes in the dependent variable. However, it is important to note that there may be other factors that also affect the dependent variable. These are called extraneous variables. It is important for experimenters to control for extraneous variables as much as possible in order to isolate the effect of the independent variable.


Let's consider an experiment to investigate the effect of sleep deprivation on memory performance. In this experiment, the independent variable would be the amount of sleep (e.g., 0 hours, 4 hours, 8 hours). The dependent variable would be memory performance, which could be measured by a test that assesses recall and recognition.

Types of Experimental Designs

There are different types of experimental designs of research. They are:

  • Pre-experimental Research Design
  • True-experimental Research Design
  • Quasi-Experimental Research Design

Pre-experimental Research Design

The simplest form of experimental research design in Statistics is the pre-experimental research design. In this method, a group or various groups are kept under observation, after some factors are recognised for the cause and effect. This method is usually conducted in order to understand whether further investigations are needed for the targeted group. That is why this process is considered to be cost-effective. This method is classified into three types, namely,

  • Static Group Comparison
  • One-group Pretest-posttest Experimental Research Design
  • One-shot Case Study Experimental Research Design

True-experimental Research Design

This is the most accurate form of experimental research design as it relies on the statistical hypothesis to prove or disprove the hypothesis. This is the most commonly used method implemented in Physical Science. True experimental research design is the only method that establishes the cause and effect relationship within the groups. The factors which need to be satisfied in this method are:

  • Random variable
  • Variable can be manipulated by the researcher
  • Control Groups (A group of participants are familiar with the experimental group, but the experimental rules do not apply to them)
  • Experimental Group (Research participants where experimental rules are applied)

Quasi-Experimental Design

A quasi-experimental design is similar to a true experimental design, but there is a difference between the two.

In a true experiment design, the participants of the group are randomly assigned. So, every unit has an equal chance of getting into the experimental group.

In a quasi-experimental design, the participants of the groups are not randomly assigned. So, the researcher cannot make a cause or effect conclusion. Thus, it is not possible to assign the participants to the group.

Apart from these types of experimental design research in statistics, there are other two methods used in the research process such as randomized block design and completely randomized design.

 Steps in experimental design process

The experimental design is a set of procedures that are designed to test a hypothesis. The process has five steps: define variables, formulate a hypothesis, design an experiment, assign subjects, and measure the dependent variable.


1. https://www.scribbr.com/methodology/experimental-design/

2. https://byjus.com/maths/experimental-designs/

3. https://study.com/academy/lesson/experimental-design-in-science-definition-method.html


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