Subject bias, also known as participant bias, is the tendency of subject or participant in a study to react, either consciously or unconsciously, in a manner that they think that the experimenter wants, rather than to respond naturally. This is a common side-effect when subjects are aware of the purpose of the study. This problem can be averted by not making the subjects aware of the true object of the study, or by the use of covert surveillance. The previous method, if being studied by questionnaire, may include questions that have no actual bearing on the study. The latter, the covert surveillance method, means observing all behaviors while counting only the behaviors that pertain to the study.