Planning the Experimental Design
Categories of Experiments
Parallel Group Design
The parallel group design involves three or more groups that initially have identical conditions but with one group designated as the control group while the others are the experimental groups. The experimenter can manipulate or create variations of the independent variable.
- In the example involving the insecticidal property of the neem tree leaves, the control group could be the use of water by means of spray technique on mosquitoes. The experimental groups would be 1:1 ratio of solute to solvent and 1:2 ratio of neem tree leaves to water.
Example:
The purpose for having a control group in an experimental design is for the experimenter to have a basis for comparing how effective the independent variable is in creating a significant physical or chemical change on the experimental units.
Preparing the Experimental Design
The following are the parts of an experimental design and the corresponding steps in preparing the design:
- Statement of Purpose: Determine what is it that you would like to investigate.
- Research Question(s): Write one or more questions that address unanswered aspects of your research topic or problem.
- Independent Variable(s): List the factor(s) that you can manipulate or control. Draw a star on the one(s) that will most likely be relevant to your investigation.
- Dependent Variable(s): List the factor(s) that respond to manipulation or control and will produce collectible data.
- Hypothesis(es): Formulate one or more statements that will predict the possible outcome(s) of your research. The statement(s) should describe how changing the independent variable will affect the dependent variable.
- Control (if applicable): Describe the standard of comparison you will use to assess experimental effects.
