Internal validity is referred to as the extent to which evidence supports a claim made by researchers regarding cause and effect, within the context of particular study design. It is referred to as one of the most important characteristics of scientific or research studies and is a significant concept in providing reasoning about evidence more generally. Internal validity is determined by how well a study provides the evidence or provide an argument for alternative explanations with respect to its findings.

 Internal validity is defined as the idea or knowledge indicating how well experiment was done, especially provide the idea of the research result whether it avoided the cofounding or not the cofounding is defined as the phenomenon when two independent variables are acting together at the same time in the research.   Many researchers suggested that the high number of cofounding in the study decreases the internal validity of the study. On the other hand, the less number of cofounding in the study indicated high internal validity of the study. Consequently, it provided the idea that whether the study is internally valid or not by looking at the cofounding in the research.  While cofounding of the study is not obvious in the study, there are various factors that help to determine the cofound. The factors include Regression to the mean, Pre-testing subjects, Changing the instrument, Participants dropping out, Failure to complete protocols and Failure to complete protocols. Many researchers suggested that regression to the mean refers to the phenomenon when subjects in the experiments with extreme score will move towards the average.  Considering Pre-testing subjects,  the researchers suggested that Pre-testing subjects may have unexpected consequences as it may be impossible to evaluate the way the pre-test and during-tests interact during the research. If “logical reasoning” is considered as a dependent variable, participants may get clues from the pre-test whether there is a cofounding or not. The changes in the instrumentation may give affect the internal validity of the research.  Participants dropping out of the study may affect the internal validity of the study.  The choice of statistics can be another factor that may impact the internal validity of the study. This is usually considered as a bigger threat for experimental designs such as randomized control trial, cohort study and any other study designs with more than one group as study participants. On the other hand, many researchers suggested that    Something unexpected changes in the study result, measurement or outcome during the experiment may affect the dependent variable which further impacts the internal validity of the research. These are the experimental biases which are determined when researchers are conducting an experiment’s and the result of the experiments strictly controlled by behavior attitude of the participants participated in the study.    However, the factors that affect the internal validity of the research can be reduced by fine-tuning the factors, especially the participants of the study.    In order to reduce the cofounding and improving the internal validity of the study, the participants can be chosen randomly by using through the use of double-blind study designs, in which the experimenter is not aware of the condition to which a participant belongs.

 One of the examples of internal validity can be provided by experiments. For example, if researchers ran an experiment in order to evaluate if mice lost weight when they exercised on a wheel.    The researchers have used good experimental practices, like random samples, and they used control variables in order to account for other things that might cause weight. In other words,   the researches considered several factors for the confounding variables that might affect your data and hence is considered as the research with high internal validity.