control of variables

• any other variables that may interfere with the IV are called extraneous variables and should be controlled where possible to minimise their infleunce on the DV. many extraneous variables are straightfoward to control such as lab lighting which are called nuisance variables that do not systematically vary with the IV. they do not confound the findings they just make it harder to detect a result
• confounding variables do change systematically with the IV. for example, personality may be a confounding variable. confouding variables affect the IV meaning changes to the DV cannot be explained as we cannot be aware of the true source
• participant reactivity is a extraneous variables where participants will try to work out the true aim of the research. this leads to demand characteristics of the experimental situation. participants may change their behaviour to fit in with experimenters intentions and aims (please U effect). this means participants behaviour is unnatural which affects the DV
• participants reactivity may lead to investigator effects. this is when the investigators behaviour effects the research outcome. this may be conscious or unconscious. for example, Coolican argues this inclused the expectancy effects and unconcious cues such as leading questions
• randomisation is the use of chance to reduce the researchers influence on the design of the investigation which helps to minimise confounding and extraneous variables. in an experiment where participants are in different conditions, they should be randomly determined. this is an alternative to counterbalancing
• extraneous variables can be subdivided into participant and situational variables. participant variables are any individual differences between participants that may affect the DV. situational variables are any features of the experimental situation that may affect the DV