Experimental Design in Research

Experimental Design in Practical Research

Definition

• Experimental design refers to the plan and structure of an experiment, including the methods and procedures used to test a hypothesis.

Types of Experimental Designs

• True Experimental Design:
  • Involves random assignment of participants to treatment or control groups.
  • Allows for causal inferences about the effect of the independent variable on the dependent variable.
• Quasi-Experimental Design:
  • Lacks random assignment of participants to groups.
  • Can still establish causal relationships, but with limitations.
• Pre-Experimental Design:
  • Lacks a control group or random assignment.
  • Often used in exploratory or pilot studies.

Key Components of Experimental Design

• Independent Variable (IV):
  • The variable being manipulated or changed by the researcher.
  • Affects the dependent variable.
• Dependent Variable (DV):
  • The variable being measured or observed.
  • Affected by the independent variable.
• Control Group:
  • A group that does not receive the treatment or intervention.
  • Provides a baseline for comparison.
• Treatment Group:
  • A group that receives the treatment or intervention.
  • Compares to the control group to measure the effect of the IV.

Threats to Internal Validity

• Selection Bias:
  • Occurs when the groups are not comparable at the outset.
  • Can be addressed through random assignment.
• Maturation:
  • Occurs when participants change naturally over time.
  • Can be addressed through control groups and longitudinal designs.
• History:
  • Occurs when external events affect the outcome.
  • Can be addressed through control groups and statistical controls.
• Testing:
  • Occurs when the measurement tool affects the outcome.
  • Can be addressed through multiple measures and controls.
• Instrumentation:
  • Occurs when the measurement tool changes over time.
  • Can be addressed through standardized measures and controls.

Experimental Design Considerations

• Sample Size:
  • Affects the power and precision of the study.
  • Should be determined based on the research question and population.
• Randomization:
  • Ensures that groups are comparable at the outset.
  • Reduces confounding variables and bias.
• Blinding:
  • Prevents participants and researchers from knowing group assignments.
  • Reduces bias and placebo effects.