Any variable apart from the IV that could affect the DV. If they are not controlled the researcher cannot be sure of which variables caused the changes in the DV.
Instructions
Direct orders. Detailed information about how something should be done or operated.
Standardised procedures
The process in which procedures used in research are kept the same
Randomisation
Presentation of trials in an experiment to avoid any systematic errors that might occur in the order of the trial might present
