Researchers often assess the internal validity of a study’s research design. An assessment of internal validity is an evaluation of the ability of a research design to provide evidence of a cause-and-effect relationship between an independent variable and a dependent variable. Often, researchers seek to conclude that a program or a treatment led to a difference in a dependent variable, but to come to that conclusion, researchers must rule out many other potential causal factors. A researcher may present a logical argument about the possible causal relationship between an independent and a dependent variable that are correlated, but absent adequate internal validity, conclusions may be questioned and alternative explanations for the relationship put forward.

Before a researcher begins a study, the researcher must ...