Extraneous variables are those variables that the experiment is not intentionally trying to study or test and cannot be controlled. There are 4 types of variables: Demand characteristics, Experimenter/Investigator Effects, Participant variables, and Situational variables.
Demand characteristics-environmental clues that cue the participant and affect his behavior
Experimenter/Investigator Effects-cues that are given to the participant by the researcher on how to behave, that unintentionally affects the outcome
Participant variables-prior knowledge or individual characteristics that could affect the outcome
Situational variables-lighting, temperature, noise
There are 4 approaches that researchers use to control extraneous variables:
Randomization-when sample size is very large, treatments are randomly assigned to the experimental groups.
Matching-This is when the different groups are distributed evenly, for example, in age, gender, income, so that the characteristics are matched up.
Experimental designs-the design of the experiment could potentially remove or reduce the impact of the extraneous variable.
Statistical Control-the use of Analysis of Covariance (ANOVA)- this refers to a statistical technique that is a combination of regression analysis and analysis of variance, in other words, it is the adjustment of the variables that could not be controlled by the experiment, i.e. extraneous variables (Miller & Chapman, 2001).
These 4 methods attempt to keep the extraneous variables in the experiment, constant across all conditions (Cherry, 2016).
Miller, G.A., & Chapman, J.P. (2001). Misunderstanding analysis of covariance. Journal of Abnormal Psychology. 110(1), 40-48. http://dx.doi.org/10.1037/0021-843X.110.1.40
Cherry, K. (2016). What is an Extraneous Variable? http://www.explorepsychology.com
Extraneous variables are any variables that you are not intentionally being researched in your study. However, when running an experiment or study, extraneous variables are variables you may not have considered, that are actually effecting the variables that you ARE testing. This can also be a variable that you didn’t consider that are actually effecting your study heavily (Grove, Gray, & Burns, 2015). Obviously, extraneous variables are undesired factors in any study, however they are known to come up. It is important to attempt to reduce the number of extraneous variables in studies to maintain the integrity of the research being conducted. One way to reduce extraneous variables is to implement random sampling or other controlled techniques in the research, like standardization (Kalton, 1968). To apply standardization to the example given in the text book, the choice including patients with abdominal incisions only, is a way to standardize the patient base for a study examining relaxation techniques in post-surgical patients. Control of extraneous variables is the way that researchers can determine the most precise results.
Grove, S., Gray, J., Burns, N. (2015). Understanding Nursing Research, 6th Edition. [Pageburstls]. Retrieved from https://pageburstls.elsevier.com/#/books/9781455770601/