A variable not part of the intended design that may affect the dependent variable is called what?

A variable not part of the intended design that may affect the dependent variable is referred to as a confounding variable. This term describes any external factor that correlates with both the independent variable and the dependent variable, which can lead to erroneous conclusions about the relationship between those two variables.

For instance, in a study examining the impact of music therapy on reducing anxiety levels, a confounding variable could be the participant’s prior experience with therapy or music. If not controlled, this could skew the results, making it seem as though the music therapy itself is solely responsible for any observed changes in anxiety levels, when in reality, the participant's background could be influencing their response.

In research design, recognizing and accounting for confounding variables is crucial to ensuring that the results are valid and can be attributed specifically to the independent variable being manipulated. This is essential in any study aiming to establish clear cause-and-effect relationships.