The extent to which a researcher devises a solid experiment, controls for confounding variables, and executes the procedure as planned determines a finding’s internal validity.

Using the vernacular of epidemiology, aging in this example is known as a confounding variable. The apparent association between living in Florida and having Alzheimer's is confounded by age. If a ...

The extent to which a researcher devises a solid experiment, controls for confounding variables, and executes the procedure as planned determines a finding’s internal validity.