Internal Validity
Definition
The degree to which a demonstration rules out explanations other than the independent variable for the change observed. High internal validity means the design controlled for confounds well enough that the treatment is the most plausible cause.
In plain language
How sure you can be that the treatment, and not something else, caused the change.
Example
A multiple-baseline shows improvement in each setting only when treatment reaches it. Maturation or a change at home cannot explain that pattern.
Not internal validity
An A-B comparison where a new medication started the same week as the plan. Either could explain the change, so internal validity is low.
Commonly confused with
See also
Written from
- kazdin-2011
Written from Kazdin (2011) on validity in single-case research. No textbook glossary consulted.
This entry has not yet been through clinical review. Treat it as a draft.