Mattson 1985.

Methods	Multicentre, randomised, parallel‐group, double‐blinded trial over 10 centres in the USA with separate randomisation schemes used for each seizure type. 4 treatment arms: CBZ, PHB, PHT and primidone
Participants	Adults with previously untreated or under‐treated simple or complex partial or secondary generalised tonic‐clonic seizures Number randomised: PHB: 155, PHT = 165, CBZ = 155 413 male participants (87%) 99.8% of participants with partial epilepsy Mean age (range): 41 (18‐82) years
Interventions	Monotherapy with PHT or CBZ Median daily dose achieved: CBZ = 800 mg/d, PHB = 160 mg/d, PHT = 400 mg/d Range of follow‐up: 0‐78 months
Outcomes	Participant retention/time to drug failure (length of time participant continued to take randomised drug) Composite scores of seizure frequency (seizure rates and total seizure control) and toxicity Incidence of side effects
Notes	IPD provided for all outcomes of this review by the Department of Veterans Affairs
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Participants randomised with stratification for seizure type. Method of randomisation not stated and not provided by authors
Allocation concealment (selection bias)	Unclear risk	No information provided
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind (participants and personnel) achieved using an additional blank tablet
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No information provided
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition rates reported, all randomised participants analysed from IPD provided (see footnote 2)
Selective reporting (reporting bias)	Low risk	Protocol provided. All outcomes reported or calculated with IPD provided (see footnote 2)
Other bias	Low risk	None identified