In an experiment, one of the most important things a researcher must focus on is the principle of validity, or the assurance that the research is actually studying what it was intended to study (Myers & Hansen, 2012). When setting up an experiment, there are two forms of validity in particular that the researcher must focus one. Firstly, the researcher must focus on internal validity. This type of validity is concerned with the assurance that the changes that were measured in the dependent variable (DV) were actually caused by the manipulation of the independent variable (IV) and not caused by any other types of extraneous variables (EV). Secondly, researchers must be concerned with their study’s external validity. External validity refers to how well the results of the study generalize to the population of interest from which the sample was pulled (Myers & Hansen, 2012). When setting up an experiment, there are several ways in which the researcher can increase both of these validity types.
For internal validity, one of the main concerns is the study’s amount of control. Control refers to the number of safeguards that were put in place in order to control for EV’s, or variables other than the IV that may have influenced or changed, the DV (Myers & Hansen, 2012). The best time to plan for these controls is during the set up of the experimental procedures. For example, researchers should ensure that they have properly defined their variables, properly set up their measuring techniques, and included enough levels of the IV to properly test their hypothesis. Additionally, in order to control for EV’s caused by subject variables, or individual differences between subjects, researchers should ensure they utilize random assignment (Myers & Hansen, 2012). Researchers can also choose to measure their internal validity after their study is over. For example, researchers can provide questionnaires, or surveys, to their subjects after the study concludes in order to investigate how the subject felt during the examination, or if they were confused during the study. These are important factors to look at as these could introduce possible EVs into the study that may have resulted in the measured behaviors (Myers & Hansen, 2012).
As mentioned above, the primary concern for external
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