Sinha 1976.

Methods	Individually randomised trial conducted in India
Participants	Eligibility: children aged 2 months to 4.5 years were eligible for inclusion in the trial. No exclusion criteria was described. Sample: 306 children were randomised either to vitamin A or placebo group in equal numbers (153 in each group)
Interventions	Children in experimental group received vitamin A in a dose of 200,000 IU every 4 months for 12 months. The comparison group received placebo only.
Outcomes	Bitot spots, side effects (vomiting)
Notes	The people in the study population were extremely poor.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The children were divided in two groups of 153 each (two of the children died in the 1st year and two left the village) and were matched for age, sex, socioeconomic status, and playmate contacts. One of the children of each matched pair was selected randomly for receiving vitamin A and the other child received a placebo." Comment: no detail about randomisation method provided
Allocation concealment (selection bias)	Unclear risk	Quote: "In a separate laboratory, the designated 2‐ml dose of vitamin A or placebo for each child was put into a vial labelled with the child's number and the vials were then shipped to the field station for distribution. Neither the clinician nor the paramedical workers, who personally fed vitamin A and placebo or examined the children for the signs and symptoms of vitamin A deficiency, knew which children received vitamin A." Comment: insufficient details provided
Blinding (performance bias and detection bias) Blinding of Participants	Low risk	Quote: "Neither the clinician nor the paramedical workers, who personally fed vitamin A and placebo or examined the children for the signs and symptoms of vitamin A deficiency, knew which children received vitamin A." Comment: probably done.
Blinding (performance bias and detection bias) Blinding of provider	Low risk	Quote: "Neither the clinician nor the paramedical workers, who personally fed vitamin A and placebo or examined the children for the signs and symptoms of vitamin A deficiency, knew which children received vitamin A." Quote: "The placebo consisted of deodorized arachis oil which was coloured and favoured with orange to match exactly the vitamin A preparation." Comment: provider blinded
Blinding (performance bias and detection bias) Blinding of outcome assessor	Low risk	Quote: "Neither the clinician nor the paramedical workers, who personally fed vitamin A and placebo or examined the children for the signs and symptoms of vitamin A deficiency, knew which children received vitamin A."
Incomplete outcome data (attrition bias)	Unclear risk	Comment: based on the outcome data reported, it does not seem that any children dropped out (i.e. there were no losses); however, this could be because the authors are conducting an intention‐to‐treat analysis but never say so. They are not explicit in this regard, as such the risk of bias due to incomplete outcome data is unclear.
Selective reporting (reporting bias)	Unclear risk	Comment: does not reference a protocol or trial registration number and does not state that all measured outcomes are reported.
Other bias	Low risk	Comment: no other apparent bias