Scientific studies play an important role in expanding knowledge and allowing mankind to understand the universe. One of the issues that these studies examine is the association between different factors. For example, scientists may wish to determine if a certain factor is responsible for a particular observation. To ensure that the results of such studies are reliable, scientists need to ensure internal validity. Essentially, internal validity allows scientists to confirm that the dependent variable being investigated is indeed responsible for the changes in the independent variable (Rubin & Babbie, 2009). Thanks to internal validity, scientists can rule out that other extraneous factors are responsible for the observations that have been made.
Control group and internal validity
One of the tools that allow for internal validity to be achieved is a control group. In many cases, the control group is not subjected to the same intervention that the treatment group receives. This is deliberate and is intended to ensure that the dependent variables under investigation are indeed responsible for the observations made (Gravetter & Forzano, 2009). Thanks to the control group, those conducting an experiment can confidently conclude that their observations were not the result of some extraneous factors. That scientists usually include control groups in their studies is clear indication that they recognize the numerous threats to internal validity. Without a control group, it is very difficult to confidently claim that the observations made are the result of the action of the variables in question. Therefore, the presence of a control group serves to account for the threats to internal validity.
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Threats to internal validity
There are a number of threats that scientists face in their efforts to achieve internal validity. Some of these threats can be tackled using a control group. Selection bias is among these threats. Basically, this threat occurs when subjects are self-selected and the assignment to the experimental and control groups is not conducted randomly (Polit & Beck, 2008). A random selection process allows for this threat to be addressed. History is yet another threat that can be tackled using a control group. History refers to events in the past which could affect the outcome of the study. Since the subjects in both the control and experimental group have been subjected to the same historical events, the scientists can rule out that these events shaped the results of the study.
Maturation is another factor that poses a threat to internal validity. This threat is said to have occurred when some normal processes of development affect the result of a study (Polit & Beck, 2008). A control group allows scientists to minimize this threat because the control group and the experimental group are subject to the same development process. Basically, the control group allows the scientists to control for maturation. Design contamination also poses a threat to the validity of studies. It occurs when subjects participate in the study with the goal of causing certain events (O’Sullivan et al., 2016). For example, a subject may seek to cause a negative link between the dependent and independent variables to be established. As they randomly assign subjects to the control and experimental groups, scientists make it nearly impossible for design contamination to occur.
In addition to the threats discussed above, statistical regression also hinders the efforts of scientists to obtain reliable and valid results. Essentially, the threat of statistical regression becomes real when the scientist recruits subjects whose differences are so massive that it is difficult to ensure that these differences do not affect how the subjects perform in the study (Beins, 2017). Usually, scientists strive to recruit subjects who share similarities. The scientists also try to minimize the impact of any differences. The random assignment of the subjects to the control and experimental groups aids the efforts of the scientists to achieve internal validity. In conclusion, control groups are undoubtedly vital as they guarantee internal validity. They enable scientists to establish with certainty that the observations that they make are the result of the variables that they are investigating. Since the control groups are important, scientists should incorporate them into their studies.
References
Beins, B. C. (2017). Research Method: A Tool for Life. Cambridge: Cambridge UniversityPress.
Gravetter, F. J. & Forzano, L. B. (2009). Research Methods for Behavioral Sciences. Boston: Cengage Learning.
O’Sullivan, E., Rassel, G., Berner, M. & Taliaferro, J. D. (2016). Research Methods for Public Administrators. London: Taylor & Francis.
Polit, D. F. & Beck, C. T. (2008). Nursing Research: Generating and Assessing Evidence For Nursing Practice. Philadelphia, PA: Lippincott Williams & Wilkins.
Rubin, A. & Babbie, E. R. (2009). Essential Research Methods for Social Work. Boston: Cengage Learning.
