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Control of variables - Coggle Diagram
Control of variables
Extraneous variables
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 straightforward to control such as the age of the participants, the lighting in the lab, etc.. These are described as nuisance variable' that do not vary systematically with the IV. These may 'muddy' the experimental water so to speak but do not confound the findings of the study. They may just make it harder to detect a result.
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Demand characteristics
Participants are not passive within experiments and are likely to be spending much of their time trying to make sense of the new situation they find themselves in. As such, participant reactivity is a significant extraneous variable in experimental research and one that is not very difficult to control.
In the research situation, participants will try to work out what is going on. Certain clues may help them interpret what is going on. These clues are the demand characteristics of the experimental situation and may help the participant to 'second guess' the experimenter's intentions as well as the aims of the study.
Participants may also look for clues to tell them how they should behave in the experimental situation. They may act in a way they think is expected and over-perform to please the experimenter )the please-U effect), or, they may deliberately under-perform to sabotage the results of the study (the screw-U effect). Either way, participant behaviour is no longer natural - an extraneous variable that may affect the DV.
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Randomisation
In any investigation, There are simple steps that the research can take to minimise the effect of extraneous/confounding variables on the outcome. One of these is the use of randomisation, which refers to the use of chance wherever possible to reduce the researcher's influence on the design of the investigation. In short, this is an attempt to control investigator effects.
For example, a memory experiment may involve participants recalling words from a list. The order of the list should be randomly generated so that the position of each word is not decided by the experimenter.
If there is more than one condition, the order of these conditions should be randomly determined. If all participants were able to take part in every condition, the order in which these conditions were completed would need to be randomised for each participant (this is an alternative to counterbalancing).
Standardisation
As far as is possible within an investigation, all participants should be subject to the same environment, information and experience. To ensure this, all procedures are standardised, in other words these is a list of exactly what will be done in the study. This included standardised instructions that are read to each participant. Such standardisation also means that non-standardised changes in procedure do not act as extraneous variables.