Dental movement acceleration: Literature review by an alternative scientific evidence method

Table 2 Oxford centre for evidence-based medicine 2011 levels of evidence

Question	Step 1 (Level 11)	Step 2 (Level 21)	Step 3 (Level 31)	Step 4 (Level 41)	Step 5 (Level 5)
How common is the problem?	Local and current random sample surveys (or censuses)	Systematic review of surveys that allow matching to local circumstances2	Local non-random sample2	Case-series2	N/A
Is this diagnostic or monitoring test accurate? (Diagnosis)	Systematic review of cross sectional studies with consistently applied reference standard and blinding	Individual cross sectional studies with consistently applied reference standard and blinding	Non-consecutive studies, or studies without consistently applied reference standards2	Case-control studies, or “poor or non-independent reference standard2	Mechanism-based reasoning
What will happen if we do not add a therapy? (Prognosis)	Systematic review of inception cohort studies	Inception cohort studies	Cohort study or control arm of randomized trial1	Case-series or case-control studies, or poor quality prognostic cohort study2	N/A
What are the COMMON harms? (Treatment Harms)	Systematic review of randomized trials or n-of-1 trials	Randomized trial or observational study with dramatic effect	Non-randomized controlled cohort/follow-up study2	Case-series, case-control studies, or historically controlled studies2	Mechanism-based reasoning
What are the RARE harms? (Treatment Harms)	Systematic review of randomized trials, systematic review of nested case-control studies, nof-1 trial with the patient you are raising the question about, or observational study with dramatic effect	Individual randomized trial or (exceptionally) observational study with dramatic effect	Non-randomized controlled cohort/follow-up study (post-marketing surveillance) provided there are sufficient numbers to rule out a common harm. (For long-term harms the duration of follow-up must be sufficient)2	Case-series, case-control, or historically controlled studies2	Mechanism-based reasoning
Is this (early detection) test worthwhile?	Systematic review of randomized trials or n-of-1 trial	Randomized trial or (exceptionally) observational study with dramatic effect
Is this (early detection) test worthwhile? (Screening)	Systematic review of randomized trials	Randomized trial	Non-randomized controlled cohort/follow-up study2	Case-series, case-control, or historically controlled studies2	Mechanism-based reasoning

¹Level may be graded down on the basis of study quality, imprecision, indirectness (study PICO does not match questions PICO), because of inconsistency between studies, or because the absolute effect size is very small. Level may be graded up if there is a large or very large effect size;

²As always, a systematic review is generally better than an individual study. OCEBM Levels of Evidence Working Group. “The Oxford 2011 Levels of Evidence”. Oxford Centre for Evidence-Based Medicine. http://www.cebm.net/index.aspx?o=5653.