Threats to Internal Validity. What are some specific examples of these confounding effects?

Threats to Internal Validity
Student’s Name
Institutional Affiliation
Threats to Internal Validity
Internal validity deals with how well an experiment has been carried out, more specifically by avoiding the effects of more than one independent variable. For an experiment to have higher internal validity, it must have fewer chances for other independent variables affecting the experiment. Internal validity focuses on the degree to which the design of the study can be controlled. Internal validity is determined by exerting the degree of control over potential extraneous variables. It is necessary to control these potentially confounding variables since it helps to reduce the possibility for another explanation for treatment effects to emerge as an alternative and also provides much confidence that the independent variable affects the dependent variable. There are various ways in which internal validity can be threatened. There are eight threats to internal validity, however, this essay will focus on three of them which include history, testing and regression to the mean.
History acts as a threat to internal validity in cases where other events occur beyond the researcher's control and affect the study (Rubin & Babbie, 2009). These external factors are not linked to the study and therefore interfere with the overall results of the study and the final conclusions (Rubin & Babbie, 2009). There are several examples that can illustrate history as a threat to internal validity. For example, in a study to determine the effects of alcohol on judgement, participants took part in a short test during a sober state and when drunk. The participants did well when sober and poorly performed when drunk. However, they also mixed alcohol with cigarettes and other with pills which made it difficult for the researcher to conclude that the alcohol mainly influenced their score. The consumption of other drugs apart from alcohol can be regarded as external independent variables and since they have similar effects on an individual, it would be difficult to ignore them during the study.
Testing is also a threat to internal validity in that repeated tests might lead to changes in the test scores and resultantly affect the overall conclusion (Myers & Hansen, 2011). In cases where the researcher conducts a significant number of tests on the same set of data, there is a higher possibility for the researcher to make conclusions based on false information gotten from the repeated test. For example, in a study to help students improve their etiquette, they were asked to provide responses to ten questions retrieved from common school scenarios. The researcher conducted 5 repeated tests and recorded the results...