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Table 1 Evidence grading scheme for these guidelines

From: Guidelines on the diagnosis and management of the progressive ataxias

Level of evidence [7]
 I Evidence obtained from a systematic review of all relevant randomised controlled trials.
 II Evidence obtained from at least one randomised controlled trial.
 III-a Evidence obtained from one or more controlled trials, pseudo-randomised by alternate allocation, birth date or other planned method.
 III-b Evidence obtained from prospective or retrospective cohort studies with concurrent controls, case-control studies, or interrupted time-series with a control group.
 III-c Evidence obtained from cohort studies with historical controls, two or more single-arm studies, or interrupted time-series without a parallel control group.
 IV Evidence comprises opinions based on clinical experience, descriptive studies or reports by clinical bodies or committees.
Grading of recommendations [8]
 A Body of evidence can be trusted to guide practice; includes one or more level I studies, or several at level II directly applicable to the target population, and demonstrating overall consistency of results.
 B Body of evidence can be trusted to guide practice in most situations; includes one or two studies rated as level II or several level III studies, directly applicable to the target population, and demonstrating overall consistency of results.
 C Body of evidence provides some support for recommendation(s) but care should be taken in its application; includes studies rated as III-c, or level I or II with a moderate risk of bias, some inconsistency and applicable to target population with caveats. Population studied is not the target population, however, it would make sense clinically to apply this evidence to target population.
 D Body of evidence is weak and recommendation must be applied with caution; includes level IV, or level I to IV studies with high risk of bias, inconsistent evidence and that are not applicable to target population.
 GPP Good practice point: Recommended best practice based on clinical experience and expert opinion.