Extraneous Variables (or Intervening variable) are undesirable variables that influence the relationship between the variables that an experimenter is examining. These variables are undesirable because they add error to an experiment. A major goal in research design is to decrease or control the influence of extraneous variables as much as possible.
E.g. What is the students' performance (DV) when CLT (communicative language teaching) (IV) is applied to teaching grammar?
=> motivation, tiredness, boredom, preference for the instructor's teaching style, the student's learning style are extraneous variables
