Muscle Study Group 2004.

Methods	Randomised, double‐blind, placebo‐controlled, parallel‐group trial
Participants	30 randomised participants (11 female) IFN beta‐1a (Avonex)‐treated group mean age: 64.9 ± 6.9 years; age at onset: 57.5 ± 8.4 years Placebo‐treated group mean age: 64.9 ± 7.3 years; age at onset: 55.5 ± 7.1 years Inclusion and Exclusion criteria as per Muscle Study Group 2001
Interventions	IFN beta‐1a versus placebo for 24 weeks
Outcomes	As per Muscle Study Group 2001
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The investigators reference a random component in the sequence generation process: "Randomization procedures were identical to those used in our previous trial"
Allocation concealment (selection bias)	Low risk	Central allocation: "...only the biostatistics programmer and site pharmacists had access to the treatment assignments"
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Insufficient information to permit judgement: active treatment injections may have been more likely to cause local reactions; all participants treated with non‐steroidal anti‐inflammatory drug to mask systemic reactions from active compound.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Insufficient information to permit judgement: blinding of assessors not described fully following allocation concealment.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Number of participants randomised and reasons for missing data stated; intention‐to‐treat principle stated, although data from only 1 of 3 dropouts were carried forward for analysis.
Selective reporting (reporting bias)	Low risk	The study protocol is not available, but outcomes prespecified in the methods are all reported in the results.
Other bias	Unclear risk	Insufficient information to permit judgement, but potential carry‐over effect of previous treatment(s), although inclusion criteria as per their previous study specified that participants must not have received immunosuppressive agents for at least 3 months prior to enrolment.