Internal validity in rehabilitation research.

In experimental research, internal validity is the extent to which the researcher can conclude that the manipulation of the independent variable caused change in the dependent variable. Without causal inference, researchers and research consumers would not be able to meaningfully interpret the results of experiments. This article discusses (a) threats to internal validity in rehabilitation research an (b) experimental procedures that can aid rehabilitation researchers in maximizing the internal validity of their investigations. [ABSTRACT FROM AUTHOR]