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Table 1 Rating system for risk of bias of individual studies

From: Functional electrical stimulation cycling exercise after spinal cord injury: a systematic review of health and fitness-related outcomes

Level 1 ∙ Randomised controlled trials with Low risk of bias as assessed by RoB 2.0
Level 2 ∙ Randomised controlled trials with Some concerns or High risk of bias as assessed by RoB 2.0
∙ Non-randomised controlled trials (including case–control, prospective and retrospective cohort studies) with Low or Moderate risk of bias as assessed by ROBINS-I
Level 3 ∙ Non-randomised controlled trials (including case–control, prospective and retrospective cohort studies) with Serious or Critical risk of bias as assessed by ROBINS-I
∙ Pre-post studies (any Downs and Black score)
Level 4 ∙ Case series defined by 3–5 individuals only (any Downs and Black score)
∙ Case report defined by 1–2 individuals only (any Downs and Black score)
∙ Cross-sectional controlled study (any Downs and Black score)
  1. RCTs assessed with Cochrane’s Risk of Bias (RoB) 2.0 [21], non-RCTs with Cochrane’s The Risk Of Bias In Non-randomized Studies—of Interventions (ROBINS-I) tool [22], and all other study designs using a modified version of the Downs and Black scale which ranges from 0 to 28 points [23, 24]. Further details on risk of bias assessment: https://osf.io/u9mvx/