Extraneous variables 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 (Psychology World, 2017).
The extraneous variables can be held constant by creating a standardized environment and procedure so that all variables are the same in each condition and cannot be confused. These variables exist in all studies and can interfere with obtaining a clear understanding of the relationships among the study variables.
For example, if a study focused on the effect of relaxation therapy on the perception of incisional pain, the researchers would have to control the extraneous variables, such as type of surgical incision and time, amount, and type of pain medication administered after surgery, to prevent their influence on the patient’s pain perception. Selecting only patients with abdominal incisions who are hospitalized and receiving only one type of pain medication intravenously after surgery would control some of these extraneous variables. Controlling extraneous variables enables researchers to determine the effects of an intervention or treatment on study outcomes more accurately (Grove, Gray & Burns, 2015).
To control an extraneous variable the research needs to identify those variables that are most likely to influence the dependent variable. This is done based on the researcher’s common sense, logical reasoning, and past experiences. For example, being in a loud room can cause distraction to people taking a test than that of a quieter room. So, using a quiet room, you are inhibiting the extraneous variable of noise. Furthermore, once identifying an extraneous variable they can be controlled by either holding a variable constant or matching value across treatment conditions (Psychology World, 2017).
Extraneous independent variables can be very hard, or even impossible in some situations, to control and can have an influence on the result or dependent variable. One example of this is when the subjects are people. Inclusion criteria help to eliminate some inconsistencies in subjects; however exclusion criteria must be relatively broad simply out of necessity. Every person is different and finding a sample of individuals with all of the same demographic, personal history, and family history is usually not possible.
There are many methods to reduce the effect that extraneous variables have on the dependent variable. Grove, Gray, & Burns (2015, p. 38) state “Laboratories, research or experimental centers, and test units in hospitals or other healthcare agencies are highly controlled settings in which experimental studies are often conducted. This type of setting reduces the influence of extraneous variables, which enables the researcher to examine the effect of one variable on another accurately.” In these types of facilities attempts are made to control the environmental factors such as lighting, temperature, noise level, etc. Regardless of the cause and the method to control extraneous variables, researchers should be aware that these variables can influence or skew results. “Researchers need to consider the extraneous variables identified during data collection, data analysis, and interpretation. They should also note these variables in the research report so that future researchers can be aware of and attempt to control them (Grove, Gray, & Burns, 2015, p. 311).