Schwab 1998.

Methods	Randomised controlled trial
Participants	75 participants with sudden hearing loss with at least 20 dB loss in 1 or more frequencies and/or tinnitus, seen within 2 weeks and without any prior therapy
Interventions	Control (38): no treatment HBOT (37): 100% oxygen at 1.5 ATA for 45 minutes daily, 5 days each week for 2 to 4 weeks (10 to 20 sessions)
Outcomes	Audiometric hearing and tinnitus improvement
Notes	Rank 1 for sample size: power > 80% to detect an increase in proportion of participants with significant return of hearing
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No description of allocation sequence "75 patients were randomly assigned to one of two treatment groups"
Allocation concealment (selection bias)	Unclear risk	No mention of attempt to conceal allocation
Blinding (performance bias and detection bias) All outcomes	High risk	No attempt to blind any party
Incomplete outcome data (attrition bias) All outcomes	High risk	This trial did not report results for seven participants with ISSHL and 11 with tinnitus. No strategy for dealing with this was identified
Selective reporting (reporting bias)	Low risk	No indication of missed outcomes
Other bias	Low risk	No other obvious source of bias