Michael 1993.

Study characteristics
Methods	Randomised, controlled, double‐blind, active‐control study of participant with refractory focal seizures Pre‐randomisation baseline period: 12 weeks Duration of treatment: 14 weeks. Efficacy was determined at the end of the acute phase. At the end of the 14‐week double‐blind phase, participants entered an extension phase, in which low stimulation participants were switched to high stimulation.
Participants	A multicentre trial (USA) 22 people randomised High stimulation group: 10 participants Low stimulation group: 12 participants Mean age 32 years (range 15 to 56); seizure frequency 2 per day; mean duration of epilepsy 19 years (range 5 to 32)
Interventions	Comparison of high (output current 1.0 to 3.0 mA, on/off time 30 s/5 min, frequency 30 Hz, pulse width 500 µs) and low (output current 0.25 to 0.5 mA, on/off time 30 s/60 to 90 min, frequency 1 Hz, pulse width 130 µs) stimulation in treatment of refractory focal seizures All participants had an identical implantation of the vagus nerve stimulation device (NeuroCybernetic Prosthesis, Cyberonics).
Outcomes	Primary outcome: seizure frequency (mean seizure frequency percent reduction) Secondary outcomes: Treatment withdrawal Adverse events
Notes	Supported by Cyberonics, Inc., Webster, TX
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of randomisation not specified
Allocation concealment (selection bias)	Unclear risk	No information provided
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	No details provided
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No details provided. Identical implants used.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants were included in the analysis.
Selective reporting (reporting bias)	Unclear risk	Protocol unavailable, but it appeared all expected and prespecified outcomes were reported.
Other bias	Unclear risk	All studies were sponsored by Cyberonics, the manufacturer of the device.