Shakespeare’s play Hamlet contains two psycological experiments. The first experiment tests Hamlet’s hypothesis that his uncle killed his father. Hamlet gets a group of actors to perform a play, acting out how he assumes his father was murdered. Horatio watches the reactions of the king and the rest of the audience to the play, thus serving as a reliability check on Hamlet’s observations. Thus, the independent variable is the play and the dependent varible is the reactions of the audience (including the king) to the play. Polonius’s experiment tests the hypothesis that Hamlet has become mad because of unrequited love for Ophelia. The king and Polonius observe from their secret hiding place as Hamlet unexpectedly encounters Ophelia. The presence of Ophelia is the independent variable, and Hamlet’s reaction the dependent variable.