Module 2: Overview of Experimental Designs 

Essential questions 

What differentiates experimental study from other types of research?

What are the typical steps in preparing experimental design? 

Experimental research aims at discovering causal relationship between the treatment and its outcome. It is not simply that one causes another but the certainty that nothing else causes the effect that is ultimately important in experiments. This requires a researcher to maintain control over all known factors that can affect the outcome of the experiment.

Besides discovering relationship between cause and effect, a researcher is interested in learning how much cause is necessary to produce certain effect. That is how the independent variable affects the dependent variable. This may include testing the varying degrees of independent variable or removing it altogether.

The following video illustrates these points:

Experimental design is a conceptual framework for the experiment. It is a plan of the procedures that enable us to test a hypothesis by conducting experiment and reaching valid conclusions based on the relationship between independent and dependent variables.

In experimental study, a researcher is expected:

• Identify and define a problem and goal of study
• Formulate the testable idea (hypothesis) related to the problem, and deduce its consequences
• Create an experimental design to test this hypothesis. It should include all elements of the system, conditions, and known relations of the elements
• Conduct the experiment
• Record raw data, reduce it to usable form and analyze
• Use the appropriate statistical test of significance.

Experimental design is created in advance of conducting the actual experiments, and typically it includes the following steps:

• Selection of subject species and sample(s)
• Selection of groups of subjects
• Identification of non-experimental factors and their control
• Selection or construction of appropriate instruments that measure experimental outcomes, and their validation
• Determination of location, time, and duration of experiments.

Unlike any other types, experimental research design relies on the random assignment of subjects to interventions/treatments. This eliminates spurious associations that can frequently impact less powerful research designs.

Suggested readings

Zacks S. (1996) "Adaptive Designs for Parametric Models". In: Ghosh, S. and Rao, C. R., (Eds). "Design and Analysis of Experiments," Handbook of Statistics, Volume 13. North-Holland. 

Creswell J.W. (2008) Educational research: Planning, conducting, and evaluating quantitative and qualitative research (3rd edition), Upper Saddle River, NJ: Prentice Hall.

Festing M. F. W. (2003) Principles: The need for better experimental design. Trends in Pharmacological Sciences. – 24 (7), p. 341-345.