Table 5.
Grading the top-cited articles in inflammatory bowel disease according to the Oxford Centre for Evidence-Based Medicine levels of evidence
| Level | Domain | Characteristics and description | Articles number (references) |
| 1a | Therapeutic/prevention, aetiology/harm | Systematic reviews of RCTs (with consistent results from individual studies) | 133 |
| Prognosis | Systematic reviews with homogeneity of inception cohort studies | ||
| Diagnosis | Systematic reviews with homogeneity of level 1 diagnostic studies | ||
| Differential diagnosis/symptom prevalence study | Systematic reviews with homogeneity of prospective cohort studies | ||
| 1b | Therapeutic/prevention, aetiology/harm | Individual RCT (with narrow CIs) | 1224 26 30 47 50 52 53 56 58 59 66 67 |
| Prognosis | Individual inception cohort study with >80% follow-up | ||
| Diagnosis | Validating cohort study with good reference standards | ||
| Differential diagnosis/symptom prevalence study | Prospective cohort study with good follow-up | ||
| 2a | Therapeutic/prevention, aetiology/harm | Systematic review of cohort studies (with consistent results from individual studies) | 234 63 |
| Prognosis | Systematic review with homogeneity of either retrospective cohort studies or untreated control groups in RCT | ||
| Diagnosis | Systematic review with homogeneity of level 2 diagnostic studies | ||
| Differential diagnosis/symptom prevalence study | Systematic review with homogeneity of 2b and better studies | ||
| 2b | Therapeutic/prevention, aetiology/harm | Individual cohort study (including low-quality RCT, eg, <80% follow-up) | 331 46 49 |
| Prognosis | Retrospective cohort study or follow-up untreated control patients in an RCT | ||
| Diagnosis | Exploratory cohort study with good reference standards | ||
| Differential diagnosis/symptom prevalence study | Retrospective cohort study or poor follow-up | ||
| 2c | Therapeutic/prevention, aetiology/harm | Outcome studies (analysis of large registries) | 338 60 61 |
| Prognosis | Outcomes research | ||
| Diagnosis | |||
| Differential diagnosis/symptom prevalence study | Ecological studies | ||
| 3a | Therapeutic/prevention, aetiology/harm | Systemic reviews of case-control studies (with consistent results from individual studies) | 925 27 35 36 41 43 45 55 57 |
| Prognosis | |||
| Diagnosis | Systematic reviews with homogeneity of 3b and better studies | ||
| Differential diagnosis/symptom prevalence study | Systematic reviews with homogeneity of 3b and better studies | ||
| 3b | Therapeutic/prevention, aetiology/harm | Individual case-control study | 1520–22 28 29 32 40 42 44 51 54 62 64 65 68 |
| Prognosis | |||
| Diagnosis | Non-consecutive study, or without consistently applied reference standards | ||
| Differential diagnosis/symptom prevalence study | Non-consecutive cohort study or very limited population | ||
| 4 | Therapeutic/prevention, aetiology/harm | Case series (and poor quality cohort and case-control studies) | 523 37 39 48 69 |
| Prognosis | Case-series (and poor quality prognostic cohort studies) | ||
| Diagnosis | Case-control study, poor or non-independent reference standard | ||
| Differential diagnosis/symptom prevalence study | Case-series or superseded reference standards | ||
| 5 | Therapeutic/prevention, aetiology/harm | Expert opinion without explicit critical appraisal or based on physiology, or bench research | 0 (0) |
| Prognosis | Expert opinion without explicit critical appraisal or based on physiology, or bench research | ||
| Diagnosis | Expert opinion without explicit critical appraisal or based on physiology, or bench research | ||
| Differential diagnosis/symptom prevalence study | Expert opinion without explicit critical appraisal or based on physiology, or bench research |
RCT, randomised controlled trial.