An extraneous variable is any variable that is not one of the independent variables in a study but might still influence the dependent variable. If not controlled, extraneous variables can introduce noise, increase variability, or even become confounding variables if they systematically differ across groups, potentially distorting the study’s conclusions.
A nuisance variable is a specific type of extraneous variable that researchers identify as a potential source of unwanted variation and deliberately control for in the study design or analysis. While nuisance variables can add variability to the results, they are typically not of primary interest and are not confounders, meaning they do not interact meaningfully with the independent variables.
For example, in a study testing a new teaching method, differences in classroom temperature across groups could be an extraneous variable that affects student performance. If the researchers anticipate this and control for temperature, it would be considered a nuisance variable.