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Please write a paragraph responding to the discussion bellow. Add citations and references in alphabetical order.

Extraneous Variables are undesirable variables that influence the relationship between the variables that an experimenter is examining. In other words, these are variables that influence the outcome of an experiment, though they are not the variables that are actually of interest. 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. One of the most common types of confounding occurs when an experimenter does not or cannot randomly assign participants to groups, and some type of individual difference (e.g., ability, extroversion, shyness, height, weight) acts as a confounding variable. For example, let’s say that an educational psychologist has developed a new learning strategy and is interested in examining the effectiveness of this strategy. The experimenter randomly assigns students to two groups. All of the students study text materials on a biology topic for thirty minutes. One group uses the new strategy and the other uses a strategy of their choice. Then all students complete a test over the materials. One obvious confounding variable in this case would be pre-knowledge of the biology topic that was studied. This variable will most likely influence student scores, regardless of which strategy they use. Because of this extraneous variable (and surely others) there will be some spread within each of the groups. It would be better, of course, if all students came in with the exact same pre-knowledge. However, the experimenter has taken an important step to greatly increase the chances that, at least, the extraneous variable will add error variance equivalently between the two groups. That is, the experimenter randomly assigned students to the two groups.

Extraneous variables should be controlled if possible. One way to control extraneous variables is with random sampling. Random sampling does not eliminate any extraneous variable, it only ensures it is equal between all groups. If random sampling is not used, the effect that an extraneous variable can have on the study results becomes a lot more of a concern (explorepsycology, 2018).


Extraneous Variables. (n.d.). Retrieved from