Hall 2006 (Cluster)

Methods	Cluster‐RCT Method to adjust for clustering: not adjusted (review authors adjusted using the ICC from Alderman 2006) Cluster unit: school Average cluster size: 33 ICCs: not reported Length of follow‐up: 2 years
Participants	All children living in endemic area Number analysed for primary outcome: 80 schools randomized containing 2659 children in class 3 Mean age: 104.5 months Inclusion criteria: children from class 3 and born in 1990 of 80/81 schools in the Red River delta of north Vietnam Exclusion criteria: none stated
Interventions	Multiple doses vs placebo Albendazole (GlaxoSmithKline): 400 mg every 6 months and 200,000 IU retinol after first 6 months only; Retinol: 200,000 IU after first 6 months followed by inert placebo every 6 months.
Outcomes	Measured: Hookworm, Trichuris, and Ascaris prevalence; Eggs/g faeces; Weight and height; Mathematics test score, Vietnamese test score.
Notes	Location: Vietnam Community category: 1 It is unclear what is meant by "randomization was adjusted so that there were equal numbers of schools in each district of the trial group". It is also appears as if the analysis has not taken into account the effects of cluster randomization. Source of funding not reported.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomization was adjusted so that there were equal numbers of schools in each district of the trial group" (unclear what this means)
Allocation concealment (selection bias)	Low risk	Central allocation. "...using a list provided by the Ministry of Education".
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Placebo was used, blinding not reported.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Insufficient reporting of attrition/exclusions. 80 schools containing 56,444 pupils randomized, and those from class 3 used in trial. Inclusion of all randomized participants (number evaluable/number randomized): unclear; 80 schools containing 56,444 pupils randomized, and those from class 3 used in trial.
Selective reporting (reporting bias)	Low risk	All stated outcomes reported.
Other bias	Low risk	Although not adjusted for clustering, we used estimates to adjust in the review. Recruitment bias: low (schools) Baseline imbalance: low (characteristics similar) Loss of clusters: low (no loss reported) Incorrect analysis: not cluster adjusted (high risk) Comparability with RCTs randomizing individuals: unclear