Many phenomena can be studied with observational research. An example of observational research is making a survey of the plants and insects of a certain beach, identifying the species of these organisms and writing a report about the process and its findings.
Experimental research includes test groups and control groups. These groups are observed in order to study the validity of a certain hypothesis. For example, we can study the hypothesis "Higher amounts of nitrogen increase the growth of aquatic plants". To study the hypothesis, we can observe aquatic plants in aquariums. Ten aquariums will receive more nitrogen (test group 1), another ten will receive even more nitrogen (test group 2), and ten are left untouched (control group). To study the validity of the hypothesis, the sizes of the plants in the different aquariums will be measured over a certain period of time.
