Shankar 1999.

Study characteristics
Methods	Individually randomised trial conducted in Guinea Bissau
Participants	Eligibility: children aged 6–60 months who planned to reside within the study area for ≥ 1 year Excluded: children with ocular signs of VAD or history of night blindness Sample: 480 children; 239 in vitamin A group, 241 in control group. 51% boys
Interventions	Experimental group: vitamin A 100,000 IU for children aged < 1 year and 200,000 IU for older children + vitamin E 20 IU Control group: placebo + vitamin E 20 IU Study duration: intervention given every 4 months for 13 months
Outcomes	Incidence of diarrhoea and malaria morbidity, mean vitamin A serum levels
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Within these strata, children were individually allocated vitamin A or placebo in blocks of four (two vitamin A, two placebo) by computer generated randomly permutated codes".
Allocation concealment (selection bias)	Low risk	Quote: "Capsules were encoded into four groups; two placebo and two vitamin A, and the code was kept offsite by personnel who were not involved in the study".
Blinding (performance bias and detection bias) Blinding of participants	Low risk	Comment: identical capsules, and allocation was concealed and code kept off site; described as double‐blind.
Blinding (performance bias and detection bias) Blinding of provider	Low risk	Comment: as above; probably done.
Blinding (performance bias and detection bias) Blinding of outcome assessor	Low risk	Comment: unlikely that the trained village‐based morbidity worker knew the assignments, however, this is never stated explicitly. Probably done.
Incomplete outcome data (attrition bias)	Low risk	Quote: "Cross sectional follow‐up rates for mid‐study and end of study were 428 of 480 (89%) and 410 of 480 (85%), respectively, and similar for vitamin A and placebo groups. During the trial two children dropped out, 66 moved out of the study area, and two died". Comment: intention‐to‐treat used. Missing outcome data balanced in numbers across groups.
Selective reporting (reporting bias)	Unclear risk	Comment: protocol not referenced and not stated that all measured outcomes were reported. Data at 7 months not completely reported.
Other bias	Low risk	Comment: no other apparent bias.