any variable other than the IV that may affect the DV if isn't controlled. EVs are essentially nuisance variables that don't vary systematically with the IV.
confounding variables?
a kind of EV but the key feature is that a confounding variable varies systematically with the IV. therefore we cant tell if any change in the DV is due to the IV or confounding variable
demand characteristics?
any cue from the researcher or from the research situation that may be interpreted by participants as revealing the purpose of the investigation. may lead to particant changing their behaviour within the research situation.
investigator effects?
any effect of the investigators behaviour on the research outcome. this may include everything from the design of the study to the selection of and interaction with participants during the research process.
randomisation?
the use of chance methods to control for the effects of bias when designing materials and deciding the order of experimental conditions.
standardisation?
using exactly the same formalised procedures and instructions for all participants in a research study
