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would have to make sure that group A roughly matched group B with prior knowledge before starting the study. Other extraneous variables could include amount of support inthe home, socio-economic income, or temperature of the testing room.there are four approaches by which the effect of the extraneous variables can be controlled.1) Randomization:In this approach, treatments are randomly assigned to the experimental groups. It is assumed that the extraneous factors are present equally in all the groups. This technique is only workable when the sample size is very large.2)Matching:Another important technique is to match the different groups ofconfounding variables. Different confounding variables like gender, age, income etc. could be distributed equally amongst the group. It sometimes does become difficult to extend matching within all the groups and another drawback of the same is that, sometime the matched characteristics may be irrelevant to the dependant variable.
3)The use experimental designs:In certain studies, the experimental designs may play a crucial role in reducing or completely removing the role and impact of the extraneous variables.4)Statistical Control:There may be situations, when all the above mentioned methods to control the extraneous variables do not show any significant outcome. It brings the entire research into question as then causalinferences are difficult to make. Another method that may work to bring down the effect of extraneous variables is the method of statistical control. Among the various statistical tools and techniques, Analysis of Covariance ( ANOVA) helps in reducing the impact of the extraneous factors on the study.These four methods, in their own way, can be used in the research, collectively or exclusively to eliminate the relationship impact discussed above. It is dependent upon the expertise of the researcher to understand and administer these methods in a way that the best possible results can beobtained.For example, imagine that a researcher has devised an experiment to investigate whether giving study extra study time can help reduce test anxiety. The amount of study time the students have is the independent variable (since it is what the experimenter manipulates) and the amount of test anxiety the students experienceis the dependent variable (since it is what the researchers are measuring).When as experiment is conducted, there are other variables that can affect results if they are not control them appropriately. The researcher might want to make sure that it is the manipulation of the independent variable that has made changes in the dependent variable. Therefore, all the other variables that could affect the dependable variable to change must be controlled. These other variables are called extraneous or confounding variables.