Controlling Variables

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Extraneous Variables:

Extraneous variables are variables other than the independent variable that may affect the dependent variable. Most extraneous variables are easy to control such as age of participants or lighting in a lab. These are described as nuisance variables and may make it harder to detect a result. Extraneous variables do not vary systematically with the IV.

Confounding Variables:

Confounding variables are variables other than the IV that may have affected te DV so we cannot be sure of the true source of changes to the DV. They do change systematically with the IV. For example in the energy drink study, there were 20 participants. It may be decided that the first 10 participants that arrive are used in the water condition. It may be that these first 10 people are shy, introverted people whereas the other 10 are outgoing, loud, extroverted people. So when the results are analysed and its found that the people who drink energy drinks were more chatty, we cannot be sure if this is because of the energy dink or their personality. The personality is a confounding variable and extroversion varied systematically with the IV which could explain the changes in the DV.

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Demand Characteristics:

In an experiment participants 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 experiment and may help the participant to second guess the experimenters intentions as well as the aims of the study. Participants may also look for clues to tell them how they should behave in the experiment. They may act in a way that they think is expected and over-perform to please the experimenter, or may deliberately under-perform to sabotage the results.

Investigator Effects:

Investigator effects are effects of the investigators behaviour (conscious or unconscious) on the research outcome. For example in the energy drink experiment the investigator recording the amount of words spoken may be inclined to smile more at participants which may encourage participants to talk more, affecting the results.

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Randomisation:

Randomisation is the use of chance in order to control for the effects of bias when designing materials and deciding the order of conditions. Randomisation can help to conrol investigator effects. In an experiment where participants are involved in a number of different conditions, the order of these conditions should be randomly determined.

Standardisation:

Standardisation means using exactly the same procedures and instructions for all participants in the study. Standardisation means that non-standardised changes in the procedure do not act as extraneous variables.