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Internal validity

Internal validity refers to how well an experiment is done, especially whether it avoids confounding (more than one possible independent variable [cause] acting at the same time). The less chance for confounding in a study, the higher its internal validity is.

Therefore, internal validity refers to how well a piece of research allows you to choose among alternate explanations of something. A research study with high internal validity lets you choose one explanation over another with a lot of confidence, because it avoids (many possible) confounds.

The figure at the right summarize external and internal validity and the relation between the two. The green ellipse represents internal validity, and the blue rounded rectangle around it represents external validity,

For further explanation see asgn1g. See also: external validity