Which one of the following statements best describes the difference between an observational study and an experiment?

In an experiment the researcher is careful to determine exactly what is to be observed, whereas in an observational study there is greater concern about how the observations are made.

In an experiment the data are obtained using careful controls on the treatments, but in an observational study the data are obtained through careful observation of the responses.

In an experiment treatments are deliberately imposed upon individuals and their responses are observed. However, in an observational study without any attempt to influence the responses, individuals are observed and variables of interest are measured.

There are really no significant differences between observational studies and experiments. They are different names for essentially the same type of study.