Table 1

Level of evidence and type of study
Therapy /Prevention, Aetiology/Harm Prognosis Diagnosis Differential diagnosis/ symptom prevalence Economic and decision analysis
Investigating the effect of patient characteristic on the outcome of disease Investigating a diagnostic test. Is this diagnostic test accurate?
Level 1 Systematic Review of randomized trials(RT) Systematic Review of inception cohort studies Systematic Review of level 1 diagnostic studies Systematic Review of prospective or classic cohort Systematic Review of level 1 economic studies
High quality RT(e.g.:> 80% follow up, narrow confident interval) Individual cohort study with > 80% follow up, all patient enrolled at the same time Level 1 diagnostic studies or Validating studies which test the quality of a specific diagnostic test, previously developed, in series of consecutive patients with reference “gold” standard Prospective or classic cohort studies with good follow up (>80%) Level 1 studies (analysis based on clinically sensible costs or alternative, values obtained from many studies, and including multiway sensitive analysis
Level 2 Systematic Review of cohort studies Systematic Review of either historical cohort study or untreated control groups (control arm) in RCTs Systematic Review of level 2 diagnostic studies Systematic Review of level 2 studies Systematic Review of level 2 studies
Lesser quality RT (e.g.: <80% follow up, wide confident interval, no clear randomization, problems with blinding, etc.) Historical (retrospective) cohort study or control arm from a RCT Level 2 diagnostic studies or Exploratory studies which collect information, trawl data to find which factor are significant (e.g.: using regression analysis) Level 2 studies (retrospective or historical cohort study or with follow up <80%) Level 2 studies (analysis based on clinically sensible cost or alternative from limited studies, and including multiway sensitivity analysis.
Individual Cohort study, including matched cohort studies (prospective comparative studies) Ecological Studies
Ecological Studies
Level 3 Systematic Review of case–control studies Systematic Review of level 3 studies Systematic Review of level 3 studies Systematic Review of level 3 studies
Individual casecontrol study Level 3 diagnostic studies or studies in non-consecutive patients and without consistently reference “gold” standards Level 3 studies (non-consecutive cohort or very limited population) Level 3 studies (analysis based on poor alternative or costs, poor quality estimates of data, but including sensitivity analysis
Level 4 Case-series Case-series Case–control study Case-series No sensitivity analysis
Poor quality cohort and case–control studies* Poor quality cohort and case–control studies* Poor or non independent reference standard
Level 5 Expert opinion Expert opinion Expert opinion Expert opinion Expert opinion

A systematic review (SR) is generally better than an individual study. Experimental study (e.g.: good quality RCT) is generally better than any observational study. For observational studies : cohort study is generally better than any case–control study . A case- control study is generally better than any case- series study. * By poor quality cohort study we mean a cohort study that failed to clearly define comparison groups and/or failed to measure exposures and outcomes (preferable blinding) in the same objective way in both expose and non-exposed individuals and/or failed to identify control known confounders and/ or poor follow up. The same for poor quality case–control study except that the patients are identified based on the outcomes in this design ( e.g.: failed replant) called “cases” are compared with those who did not have the outcome (e.g.: had a successful replant) called “controls” and consequently we do not have “exposed and non-exposed” and “longitudinal follow up”. Ecological studies and Economic/decision analysis studies are very uncommon in hand surgery. This chart was adapted from material published by the Centre for Evidence-Based medicine, Oxford, Uk. March 2009.

Rosales et al.

Rosales et al. BMC Research Notes 2012 5:665   doi:10.1186/1756-0500-5-665

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