Which of the following is a true statement?
(A)While properly designed experiments can strongly suggest cause-and-effect relationships, a complete census is the only way of establishing such a relationship. (B)If properly designed, observational studies can establish cause-and-effect relationships just as strongly as properly designed experiments. (C)Controlled experiments are often undertaken later to establish cause-and-effect relationships first suggested by observational studies. (D)A useful approach to overcome bias in observational studies is to increase the sample size.
C