Planning the Experimental Design
Categories of Experiments
There are several variations to the single-factor experiment, though. These include the single group design, control group design, and parallel group design.
Single Group Design
With the single group design, you test only one independent variable against a number of experimental units. You will not make any variations, levels, or treatments but you will choose a single description for your independent variable; the description can be either qualitative or quantitative.
- For an experiment on preparing an insecticide from neem tree leaves using ethyl alcohol as solvent with a 1:2 ratio (or 50 g of neem tree leaves to 100 mL of ethyl alcohol), 50 g of neem tree leaves soaked in ethyl alcohol is the quantitative description of the independent variable.
Example:
Control Group Design
With the control group design, you include a control group, or a group that is separated from the rest of the experiment and to which nothing is done.
- In the experiment on the preparation of the insecticide from neem tree leaves, the control group would consist of only alcohol, that is, without the neem tree leaves. By comparing the neem tree leaf extract with alcohol alone, you will be able to validate the effectiveness of the leaf extract and determine if indeed alcohol will be able to extract the active insecticidal chemicals present in the neem tree leaves. Later, you will find out from data to be obtained in future experiments whether alcohol alone or an alcohol extract from neem tree leaves can kill a particular group of insects.
Example:
