Sungthong 2002.

Methods	Double‐blind, randomised, placebo‐controlled trial. 3‐arm design with individual randomisation.
Participants	Of 50 government schools located outside the municipality, selected schools had to met the following criteria: 1) high prevalence of underweight according to school‐records (no # or prevalence given to define "high"); 2) a least 150 students in school; 3) not >1 h away by car from research centre; 4) teachers willing to cooperate in study; 5) no previous iron supplementation programme implemented. Subsequently 2 schools selected. 397 school age children in grades 1‐6 (9.7 years of age in average), both sexes (212 females (53%)) only those with written parental consent included. Excluded those with severe Iron deficiency anaemia (Hb equal or lower than 80 g/L and serum ferritin equal or lower than 20 μg/L) severe malnutrition weight‐for‐height <3rd percentile of Thai reference, chronic illness such as thalassaemia, haemolytic disease and physical handicaps. Participants assigned to group stratified by anaemia status. Baseline prevalence of anaemia:˜ 35%. This study took place in a socioeconomically disadvantaged community.
Interventions	Participants were allocated to one of the following groups: Group1 (n = 134): each child received 2 bottles with tablets, the first was to be taken on Monday only while the second was to be taken for the remaining days of the week (60 mg of elemental iron (as ferrous sulphate) weekly; Group 2 (n = 140): each child received 2 bottles with tablets, the first was to be taken on Monday only while the second was to be taken for the remaining days of the week. Both bottles had 60 mg of elemental iron (as ferrous sulphate) daily); Group 3 (n = 123): Same procedure as groups 1 and 2 but children received placebo. The tablets were similar in colour, shape, size, and taste as the iron tablets. Length of the intervention: 16 weeks
Outcomes	Haemoglobin, serum ferritin, mean changes of both, height, weight.
Notes	This area is free from malaria
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Children were stratified by anaemic status to balance the proportion of anaemic and non anaemic children across the intervention groups. The children were then assigned by simple random allocation within each stratum using a computer random number generator.
Allocation concealment (selection bias)	Low risk	Tablets placed in packages labelled only with participants' name, content not known to any of the project personnel. 2 supplement packages similar in appearance: On Mondays received one packages which contained iron for daily and weekly group, but placebo for control group. Rest of week consumed tablets from other package, which were iron for daily group and placebos for weekly and placebo control group.
Blinding (performance bias and detection bias) All outcomes	Low risk	Participants: neither parents nor participants knew the content of supplement packages. Personnel: researchers did not know the content of supplement packages. Outcome assessors: not reported but probably blinded.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Only 6 of 397 enrolled lost to follow‐up.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Unclear risk	Baseline prevalence of anaemia was different among study arms (39, 40 & 28%, for daily, weekly and placebo, respectively), but haemoglobin concentrations were not statistically different.