Extraneous variables

• Key to an experiment is that the IV is manipulated to see how it affects the DV.
• the only thing that should influence the DV is the IV
• any other variables that might potentially interfere with the IV or the DV should be controlled or removed
• these additional, unwanted variables are called extraneous variables and where possible are identified at the start of the study by the researcher, who then takes steps to minimise their influence
• many extraneous variables are easy to control like age of participants and these are called nuisance variables