Ross 2007 TZA.

Methods	Trial design: cluster‐RCT Unit of randomization: communities Number of clusters: 20 Data collection: survey at 1 and 3 years after enrolment. HIV/HSV2 and pregnancy test at 3 years Length of follow‐up: 3 years Adjustment for clustering: yes
Participants	Target group: Year 5 to 7 primary school pupils (14 to 18 years old) Sample size: 9645 Exclusions: none stated
Interventions	The intervention: Did the target group receive sexuality education? Yes. How many sessions? 12 x 40 minute sessions per year for 2 years. Who delivered the sessions? Teachers with peer assistants. What was the content of the session? Aimed to provide knowledge and skills to delay sexual debut, reduce sexual risk‐taking and increase appropriate use of health services. What additional components were there? Health workers were trained for 1 week in the provision of youth‐friendly sexual and reproductive health services and supervised quarterly. Community mobilization activities included annual youth health weeks, interschool competitions and performances, and quarterly video shows. Were condoms distributed free? No, but they were promoted and sold by 4‐5 peer assistants per village. Control group: no intervention.
Outcomes	Outcomes included in this review: HIV incidence; HSV2 prevalence; syphilis prevalence; current pregnancy; self‐reported sexual debut; self‐reported condom use at last sex. Outcomes not included in this review: other self‐reported sexual behaviour such as more than 1 partner during the past 12 months.
Notes	Country: Tanzania Setting: rural areas of Mwanza region Study dates: 1998 to 2002 Study sponsors: The European Commission, Development Cooperation Ireland, UK Medical Research Council, Department for International Development (DFID)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: “Restricted randomisation was used to balance HIV and chlamydia prevalence between the two trial arms” Comment: stratified randomization of communities described; stratification explained. Source: p.1944 Methods (Ross 2007 TZA).
Recruitment bias	Low risk	Comment: individuals were recruited first and then randomized to clusters.
Baseline imbalance	Low risk	Quote: "The baseline characteristics of the intervention and comparison groups were generally similar (Table 2). Slight baseline imbalances in ethnic group and lifetime number of partners were adjusted for in all analyses of trial outcomes. There were substantial differences between male and female participants, so outcomes were analyzed separately for sex." p.1947.
Allocation concealment (selection bias)	Low risk	Quote: "A system of constrained randomisation was used to allocate communities to the two study arms,ensuring adequate balance on important factors. There were 28,000 ways of allocating half the communities in each stratum to the intervention arm. A computer program tested whether each of these allocations satisfied balance criteria, including: (i) mean HIV prevalence in each study arm within 0.075% of overall mean; (ii) mean prevalence of Chlamydia trachomatis (CT) in each arm within 0.1% of overall mean; (iii) one of two communities neighbouring gold mines allocated to each arm; (iv) even distribution of intervention communities over the four project districts. A total of 953 allocations satisfied these criteria, and one was randomly chosen at a meeting attended by senior government officials" Source: p.436 (Hayes 2005).
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: no blinding described.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: blinding was not described. Source: p.1946 Impact evaluation final paragraph. There is no description of the authors blinding the laboratory technicians to the allocation status of the samples.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: “7040 (73%) of the 9645 eligible cohort members were seen at the final survey. Follow up rates were similar in the intervention (72%) and comparison (74%) communities, higher among male (77%) than female (69%) participants (P<0.001)” “HIV incidence was much lower than predicted based on a previous survey of 15‐19 year olds in the same communities… those who were lost to follow up may have been at a higher risk than those followed up.” Comment: similar attrition across intervention and comparison groups Source: p.1497 Completeness of follow up p.1949 Table 2 p.1951 Discussion
Selective reporting (reporting bias)	Low risk	Comment: all outcomes stated in Methods were reported.
Other bias	Low risk	Comment: no other source of bias identified.