In experimental research, internal validity refers to what extent researchers can conclude that changes in the dependent variable (that is, outcome) are caused by manipulations to the independent variable. This causal inference permits researchers to meaningfully interpret research results. This article discusses internal validity threats in social and educational research using examples from the contemporary literature, and research designs in terms of their ability to control internal validity threats. An Eric and psychINFO search was performed to the current review of internal validity. The review indicated that appropriate research designs that control possible extraneous variables are needed to be able to meaningfully interpret research results in education and social sciences. Although, pretest- posttest experimental-control group design controls most of the internal validity threats, the most appropriate research design would vary based on the research questions or goals.
Key words: Internal validity, education, confounding variables, research design.