A researcher wants to evaluate the effect of using Facebook on happiness. Would an experimental or observational study design be more appropriate?

Select the correct answer below:

An experimental study should be used with the use of Facebook as the controlled factor.

An experimental study should be used with happiness as the controlled factor.

An observational study should be used because it is not possible to control the use of Facebook.

An observational study should be used because it is not possible to control happiness.