title: Checklist for the qualitative evaluation of clinical studies with particular focus on external validity and model validity.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  A checklist is presented, in which the evaluation criteria concerning external validity and model validity are systemized and transformed into a questionnaire format.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Witten/Herdecke University, Gerhard-Kienle-Weg 4, Herdecke, Germany. gudrun.bornhoeft@uni-wh.de
authors.forename: Gudrun
authors.initials: G
authors.lastname: Bornhöft
authors.forename: Stefanie
authors.initials: S
authors.lastname: Maxion-Bergemann
authors.forename: Ursula
authors.initials: U
authors.lastname: Wolf
authors.forename: Gunver S
authors.initials: GS
authors.lastname: Kienle
authors.forename: Andreas
authors.initials: A
authors.lastname: Michalsen
authors.forename: Horst C
authors.initials: HC
authors.lastname: Vollmar
authors.forename: Simon
authors.initials: S
authors.lastname: Gilbertson
authors.forename: Peter F
authors.initials: PF
authors.lastname: Matthiessen
mesh_terms: D015982:Bias; D002986:Clinical Trials as Topic / Q000379:methods / Q000592:standards*; D003627:Data Interpretation, Statistical; D005069:Evaluation Studies as Topic; D017408:Guidelines as Topic; D006801:Humans; D007258:Informed Consent; D018579:Patient Selection; D011786:Quality Control; D012015:Reference Standards; D015203:Reproducibility of Results; D012107:Research Design; D015983:Selection Bias; D016896:Treatment Outcome