Establishing the internal and external validity of experimental studies

Area of Science:

• Research Methodology
• Experimental Design
• Scientific Validity

Background:

• Internal validity ensures a study accurately reflects cause-and-effect relationships.
• External validity concerns the generalizability of study findings.
• Assessing validity is crucial for interpreting experimental results.

Purpose of the Study:

• To discuss the information required for determining internal and external validity in experimental studies.
• To present a cognitive map to guide investigators in addressing validity issues.
• To enhance the accurate portrayal of treatment effects and appropriate generalization of findings.

Main Methods:

• Discussion of internal validity concepts and threats (history, maturation, testing, instrumentation, regression, selection, mortality, interactions).
• Introduction of a cognitive map framework for evaluating validity in research reports.
• Explanation of methods to assess external validity, including inclusion/exclusion criteria and subject description.

Main Results:

• Eight specific threats to internal validity are defined.
• A cognitive map can systematically guide the assessment of internal validity issues.
• Clear delineation of criteria and subject characteristics enhances external validity.

Conclusions:

• Systematic assessment of internal and external validity is essential for accurate experimental research.
• A cognitive map provides a structured approach to address validity concerns in study reports.
• Properly addressing validity ensures reliable treatment effect portrayal and appropriate generalization.