Phil is a participant in a study designed to examine the effects of taking a new protein-containing product on muscle tissue development. Phil suspects he's in the experimental group, because he's certain his muscles are bigger and stronger as a result of taking the product supplied by the researchers. When the study is completed, Phil learns that he didn't receive the new source of protein. Phil thinks the researchers made a mistake—he's certain his muscle mass increased while he consumed the product. According to this information, Phil's belief that his physical condition improved while he participated in the study is an example of