Table 1

Classification of methodological quality of individual studies

InterventionDiagnostic accuracy of researchDamage or side effects, aetiology, prognosis*
A1Systematic review of at least two independently conducted studies of A2 level
A2Randomised double-blind comparative clinical research of good quality of sufficient sizeResearch relative to a reference test (a ‘golden standard’) with predefined cut-off points and independent assessment of the results of a test and golden standard, on a sufficiently large series of consecutive patients who all have had the index and reference testProspective cohort study of sufficient size and follow-up, at which adequately controlled for ‘confounding’ and selective follow-up sufficient is excluded.
BComparative research, but not with all the features as mentioned under A2 (this includes patient–control research, cohort study)Research relative to a reference test, but not with all the attributes that are listed under A2Prospective cohort study, but not with all the features as mentioned under A2 or retrospective cohort study or patient-monitoring research
CNot comparative research
DOpinion of experts
  • * This classification only applies to situations in which due to ethical or other reasons controlled trials are not possible to perform. If these are possible, then the classification applies to interventions.