Correlational Studies and Experiments

The purpose of experiments and studies is to examine the relationship between two different variables. In experiments, researchers manipulate a variable in a controlled environment. For example, one might monitor the amount of time it takes for different amounts of salt to dissolve in a cup of water. When performing correlational studies, however, the relationship between natural changes in variables is observed. Thus, the values of the independent variable do not necessarily change at regular intervals as they do in experiments. The diagram below helps illustrate the difference between experiments and studies.
StudyExperiment.jpg

Correlational studies are often used in place of experiments for several reasons. For one, experiments are not always feasible – we cannot force changes in gravitational forces similar to that of the moon to determine effects of such changes on ocean tides. In addition, experiments are often unethical, especially when humans or animals are involved as subjects. It would be unethical, for example, for research participants to take up smoking in order to determine effects on rates of lung cancer. Instead, researchers could recruit people who choose to smoke as part of their lifestyle and monitor health outcomes over time.

Students can solidify their understanding of experiments and studies by listing possible cause (independent) and result (dependent) variables and outline how they would study the relationship between the variables. For example, students might suggest that the relationship between number of hours spent studying per day and test scores should be observed through a correlational study. The table below contains other cause and result variables:
Cause variables
Result variables
Exercise
Muscle strength
Temperature
Crystal growth
T.V. watching
Teenager's learning
Radiation
Cancer
Time
Speed