What is an Extraneous Variable?

An Extraneous Variable is something that the experimenter cannot control, which can have an effect on the overall outcome of the experiment. The main four extraneous variables are demand characteristics, experimenter effects, participant variables and situational variables.

Demand Characteristics: Environmental clues that may tell the participant what is expected of them, such as the environmental setting or the researches body language. This in turn can affect their behaviour.

Experimenter Effects: When the researcher themselves affect the outcome by giving subconscious clues about how to behave. This may involve unintentionally asking leading questions that inform the participant of the desired result.

Participant variables: Something about the participant that is out of the researcher's control. For example, whilst researches may try and target individuals with a certain background for an experiment, existing variables such as their health, or prior knowledge, could affect the outcome. For example, a participant with prior knowledge of Milgram's experiment would be an extraneous variable in a reimagining of the experiment.

Situational variables: Whilst the researcher may do their best to control an experiment (for example, controlling the time of day), situational variables can still affect the results. For example, a field experiment conducted at the same time of day across a week may experience sporadic weather or unexpected noise pollution, changing the mood/actions of the participants.