Miller 1977c.

Methods	See Miller 1977a
Participants	20 twin pairs "low body weight"
Interventions	0.5 g/d vitamin C
Outcomes	Incidence (Analysis 1.1), duration (Analysis 2.1) and severity (Analysis 3.1)
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk
Allocation concealment (selection bias)	Low risk
Blinding of participants and personnel (performance bias) All outcomes	Low risk
Blinding of outcome assessment (detection bias) All outcomes	Low risk
Incomplete outcome data (attrition bias) All outcomes	Low risk
Vitamin C and placebo indistinguishable?	Unclear risk	?