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Open Access Highly Accessed Correspondence

Checklist for the qualitative evaluation of clinical studies with particular focus on external validity and model validity

Gudrun Bornhöft12*, Stefanie Maxion-Bergemann2, Ursula Wolf3, Gunver S Kienle4, Andreas Michalsen5, Horst C Vollmar6, Simon Gilbertson7 and Peter F Matthiessen12

Author Affiliations

1 Chair in Medical Theory, Witten/Herdecke University, Gerhard-Kienle-Weg 4, D – 58313 Herdecke, Germany

2 PanMedion Foundation, Bergstrasse 89, CH – 8032 Zürich, Switzerland

3 Institute for Complementary Medicine, University of Berne, Imhoof-Pavillon, Inselspital, CH – 3010 Bern, Switzerland

4 Institute for Applied Epistemology and Medical Methodology (IFAEMM), Schauinslandstr. 6, D – 79189 Bad Krozingen, Germany

5 Dept. for Internal and Integrative Medicine, Kliniken Essen-Mitte, Am Deimelsberg 34a, D – 45276 Essen, Germany

6 Competence Centre for General Practice and Outpatients' Health Care, Witten/Herdecke University, Alfred-Herrhausen-Str. 50, D – 58448 Witten, Germany

7 Ruhrhöhenweg 2, D-45527 Hattingen, Germany

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BMC Medical Research Methodology 2006, 6:56  doi:10.1186/1471-2288-6-56

Published: 11 December 2006



It is often stated that external validity is not sufficiently considered in the assessment of clinical studies. Although tools for its evaluation have been established, there is a lack of awareness of their significance and application. In this article, a comprehensive checklist is presented addressing these relevant criteria.


The checklist was developed by listing the most commonly used assessment criteria for clinical studies. Additionally, specific lists for individual applications were included. The categories of biases of internal validity (selection, performance, attrition and detection bias) correspond to structural, treatment-related and observational differences between the test and control groups. Analogously, we have extended these categories to address external validity and model validity, regarding similarity between the study population/conditions and the general population/conditions related to structure, treatment and observation.


A checklist is presented, in which the evaluation criteria concerning external validity and model validity are systemised and transformed into a questionnaire format.


The checklist presented in this article can be applied to both planning and evaluating of clinical studies. We encourage the prospective user to modify the checklists according to the respective application and research question. The higher expenditure needed for the evaluation of clinical studies in systematic reviews is justified, particularly in the light of the influential nature of their conclusions on therapeutic decisions and the creation of clinical guidelines.