Identification of extraneous and potentially confounding variables is a part of experimental research.
Sometimes, the dependent variable may be influenced by variables other than the independent variable. These other variables which may impact the measurement of the dependent variable are called extraneous variables (EV). Extraneous variables can come in many forms, and it is imperative to try to eliminate them in order to find the direct impact of the independent variable on the dependent variable. Again using the example of sleep and attention, an extraneous variable may come in the form of weather; one arithmetic test may be conducted in oppressive heat, whilst another may be conducted in mild temperatures. This is a variable other than the independent variable (amount of sleep) which is likely to impact the dependent variable (attention).
Further still, a confounding variable (CV) refers to any difference between results of the control and experimental groups which is caused by a variable other than the independent variable. If a study has a confounding variable, no conclusions can be made.
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