The design of any experiment is of utmost importance because it has the power to be the most rigid type of research. The design, however, is always dependent on feasibility. The best approach is to control for as many confounding variables as possible in order to eliminate or reduce errors in the assumptions that will be made. It is also extremely desirable that any threats to internal or external validity be neutralized. In the perfect world, all research would do this and the results of research would be accurate and powerful. In the real world, however, this is rarely the case. We are often dealing with human subjects, which in itself confounds any study. We are also dealing with the restraints of time and situation, often resulting in less than perfect conditions in which to gather information.
There are three basic experimental designs, each containing subsets with specific strengths and weaknesses. These three basic designs include: (1) pre-experimental design; (2) quasi-experimental design; and (3) true experimental design. They will be discussed below and as you will discover, are addressed in order of effectiveness.