West 2006.

Methods	Cluster randomisation of 16 neighbourhoods (Balozi) by using a table of random number for allocation Similar follow up periods and similar lost to follow up in the study groups, but lost to follow up 25 to 30% Outcome assessors were masked
Participants	302 children 1 to 7 years in 16 Balozi in Kongwa, Tanzania
Interventions	1. Insecticide spray (119 children in 8 Balozi) versus no intervention (183 children in 8 Balozi) for 1 year Insecticide spray with 10% permethrin
Outcomes	Prevalence of active trachoma, Chlamydia trachomatis infection rate (PCR), fly count
Notes	NCT00347763
Risk of bias
Bias	Authors' judgement	Support for judgement
Recruitment bias	Low risk	"Follow‐up rates of children in the intervention balozi were 77% at 6 months and 67% at 1 year, and 75% and 69% in controls, respectively. Children lost to follow‐up were either temporarily out of their balozi, had died, or had moved away." Results, page 598 There was no discussion of recruitment bias in the paper but the review authors made the judgement that the provision of community‐level interventions in this study (fly control) was unlikely to influence the recruitment of participants to the study
Baseline imbalance	Unclear risk	Although there was some evidence to suggest that the clusters (balozi) were similar (see quotes and data below) only 16 balozi were randomised so differences in other important confounders cannot be excluded “The mean household size did not differ between the balozi randomised to intervention and the control neighbourhoods.“ Results, page 598   “The mean number of flies in the balozi per day at baseline (measured 5 weeks before the start of spraying) did not differ between the intervention and control groups.” Results, page 598   Mean prevalence of trachoma: ‐          63% intervention; 68% control active trachoma ‐          29% intervention; 35% control ocular infection   “Trachoma and infection prevalence rates adjusted for clustering at the balozi level, period of enrolment, and potentially confounding factors of age, sex, baseline trachoma status, and antibiotic treatment.” Statistical analysis, page 598
Blinding of participants and personnel (performance bias) Active trachoma	High risk	For community based interventions such as fly control it was not feasible to mask participants and personnel and this was not described in the report
Blinding of participants and personnel (performance bias) Other outcomes	High risk	For community based interventions such as fly control it was not feasible to mask participants and personnel and this was not described in the report
Blinding of outcome assessment (detection bias) Active trachoma	Low risk	“Two graders assessed the photographs independently, masked to the intervention status and time of the examination.  [...] Outcomes are reported on the basis of masked photographic gradings" Procedures, page 597
Blinding of outcome assessment (detection bias) Other outcomes	Unclear risk	For community based interventions such as fly control it was not feasible to mask the entomological outcome assessors and this was not described in the report However, for laboratory assessment of ocular C. trachomatis infection masking should be relative straightforward however this was not described in the report
Incomplete outcome data (attrition bias) All outcomes	Low risk	“All 16 balozi initially selected were included in the trial. [...] Follow‐up rates of children in the intervention balozi were 77% at 6 months and 67% at 1 year, and 75% and 69% in controls, respectively. Children lost to follow‐up were either temporarily out of their balozi, had died, or had moved away.” Results, page 598
Selective reporting (reporting bias)	Low risk	Active trachoma and ocular infection were reported; no indication of any outcomes for which data collected and not reported