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Extraneous Variables in Experiments


There are some variables in experiments besides the independent variables that usually cause a variation or a change to the dependent variables. These variables are referred as extraneous variables in research parlance. For instance, when studying patients and their response to medication, the researchers could realize that age affects the outcomes. In addition, there are several other factors that affect research and they are not part of the independent variables. Examples include past history of the family, education, time of the day and so on.

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Main Research Variables

In nursing, just like in many other researches, there are basically two types of variables that are often included in research process. However, the research should not entirely only base the outcomes of these variables since other external factors could have a very critical impact on the experiment. Dependent and independent variables are the main factors here (Polit & Beck 2010, p. 21). Dependent variables are the factors that are of interest in experiments and are determined or predicted by the independent variables (Gay et al 2006, p. 46). For instance, a nurse could want to find out the difference in the post-operative oxygen concentration of patients in supine versus the concentration when in semi-Fowler posture. The oxygen concentration is the factor of interest and therefore the dependent variable while the position of the patient is the independent variable as it can be manipulated.

Controlling the Extraneous Variables

Since the extraneous variable can adversely impact on the outcome of the results, it is important that this variable be controlled during the process of the experiment. As the researcher plans the study, he/she should ensure that the extraneous variables are identified and controlled. For instance, when preparing to study preoperative skin progress (Polit & Beck 2010, p. 21), the researcher realizes that longer process of surgery could have an impact on the number of microbial on the skin of the participants. To control this type of variable, the investigators set the time limit for the surgery process to qualify for study (Gay et al 2006, p. 46).

There exist main methods of controlling the extraneous factors. First, there is Matching. A pair of participants from every group is matched and allowed into the study. The setback to this is lack of possible matches in some instances. Second is comparison of the homogenous groups (Duffy, 2006, p. 225). When an experiment is being carried out, similar groups are created regarding a certain extraneous variable. This is sometimes being limited by a number of scores on that type of a variable. Alternatively, the researcher can form subgroups that accommodate a bigger range of scores. Analysis of variance can be used to evaluate the way the independent variable interacts with the extraneous one. The third method is by using the analysis of co-variance to adjust the scores of dependent factors of the experiment to establish the differences with regard to the extraneous variable significance (Duffy, 2006, p. 225). The process is limited by the fact that it has to strictly comply with the many assumptions in the statistical process.


All in all the practicability of controlling extraneous variable is evident in the real research where random assignments are used. The participants are equated on all identified and anonymous extraneous variable at the beginning of the experiment. Any differences seen between the groups are plausible and can be justified. Holding one extraneous variable has been very efficient in the past. The real practice of the method requires that one variable like gender can be set constant for instance in a study of only men or women. It is almost impossible to have deferential control. However, generalization is very hard when important groups of people were excluded from the experiment systematically. Variables are the main factors of building an experiment and decisive to the research result. They hence need extensive understanding.

Reference List

Duffy, M.E. (2006). Designing Nursing Research: The Qualitative-Quantitative Debate, Journal Of Advanced Nursing, Vol. 10 Issue 3, Pages 225 – 232.

Gay L. R., Mills, G. E., & Airasian, P. (2006). Educational Research: Competencies for Analysis and Applications. (8th ed). Upper Saddle River, NJ: Pearson Education, Inc.

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Polit, D. F. & Beck, C. T. (2010). Essentials Of Nursing Research: Appraising Evidence For Nursing Practice (7th Ed.). Philadelphia, PA: Lippincott Williams & Wilkins.

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