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Table 1 Issues that potentially affect external validity adapted to Rothwell (10).

From: To whom do the results of the multicenter, randomized, controlled INSECT trial (ISRCTN 24023541) apply? - assessment of external validity

Setting of the trial  
  Healthcare system
  Recruitment from primary, secondary, or tertiary care
  Selection of participating centers
  Selection of participating clinicians
Selection of patients  
  Eligibility criteria
  Exclusion criteria
  Random ratio
  Patients declining randomization
Characteristics of randomized patients  
  Baseline clinical characteristics
  Severity of disease
Differences between trial protocol and routine praxis  
  Trial intervention
  Therapeutic or diagnostic advances since the trial was completed
Outcome measures and follow-up  
  Who measured outcome
  Frequency of follow-up
  Adequate length of follow-up
Adverse effects of treatment  
  Completeness of reporting
  Selection of trial centers/clinicians
  Intensity of trial safety procedures