Internal Validity

Internal validity refers to the accuracy of statements made about the causal relationship between two variables, namely, the manipulated (treatment or independent) variable and the measured variable (dependent). Internal validity claims are not based on the labels a researcher attaches to variables or how they are described but, rather, to the procedures and operations used to conduct a research study, including the choice of design and measurement of variables. Consequently, internal validity is relevant to the topic of research methods. In the next three sections, the procedures that support causal inferences are introduced, the threats to internal validity are outlined, and methods to follow to increase the internal validity of a research investigation are described.