What does internal validity measure?

Internal validity measures the degree to which the results of a study can be trusted to reflect the true relationship between the variables being studied within the specific group involved in the research. It assesses whether the study design, methodology, and execution effectively isolate the effects of the independent variable on the dependent variable, thereby ensuring that confounding factors do not influence the outcomes. This is crucial in determining if the findings can be attributed to the variables being tested rather than extraneous influences.

For instance, if a study aims to evaluate the efficacy of a new medication on a particular illness within a specific demographic group, high internal validity ensures that the observed effects are genuinely due to the medication itself and not other variables like age, sex, or pre-existing conditions. Thus, ensuring strong internal validity is essential for making reliable conclusions about the causal relationships within the studied group.