Experimental control helps ensure that random variables that are not under study are not influencing the results of an experiment. The experimenter needs to control all aspects of an experiment in order to ensure that any effect that is seen is caused by the independent variable. For example, time of testing, expectations of the experimenter, presentation of the independent variable all could potentially influence the outcome of an experiment. As such, each of these needs to be held constant and presented identically to each subject. This increases the reliability of the study, giving the researchers confidence that they can attribute the outcome to the independent variable alone.