Abdel-Khalik and Ajinkya (1979) provide a precise definition of the nature of an experiment in that the researcher manipulates one or more variables with subjects who are assigned randomly to various groups. These groups receive different combinations of the variables (termed treatments); in some cases a control group may exist which receives no such treatments. The major advantage of experiments lies in the researchers ability to ensure high internal validity, defined in terms of how well they can eliminate rival explanations for their results. Experiments are, thus, particularly suited to research questions that investigate causal relations between variables.

In this context, what guidelines will you suggest for a good experimental research?

Discuss the internal validity threats of experimental research.