Coyle 2001.

Methods	Design: cluster randomized trial; 20 schools assigned to study groups Location: southeast Texas and northern California, USA Time frame: 1993 to 1996 Sample size calculation (and outcome of focus): no information
Participants	General with N: 20 public schools; 3869 students in grade 9 Inclusion criteria: school districts served diverse populations (ethnicity and socioeconomic status); areas with high HIV prevalence; close to research team Exclusion criteria: no information
Interventions	Study focus: prevention of HIV, STI, and pregnancy for high school youth Theory or model: Social Cognitive Theory + social influence model and models of school change Intervention: 20 lessons (10 in grade 9; 10 in grade 10); communicating about using condoms and other contraception; school organization activities; peer resource team; parent education; school‐community linkages Comparison: standard 5‐session knowledge‐based HIV prevention curriculum plus some school activities that varied by school Duration: 2‐year program
Outcomes	Primary: frequency of unprotected sex; condom use during last sex; use of effective contraception during last sex (i.e. condom, birth control pills, or both) Secondary: attitudes about sex or condom use; HIV/STD knowledge; beliefs; self efficacy; barriers to condom use; HIV/STD risk perceptions Follow‐up: 7 months, i.e. after year 1 lessons (9th grade); 19 months, i.e. after year 2 lessons (10th grade); 31 months, i.e. 12 months after year 2 lessons
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Restricted randomization process to assign schools: schools ranked on index of possible confounders, and adjacent schools in ranking paired and randomly assigned to intervention or control
Allocation concealment (selection bias)	Unclear risk	Schools identified prior to randomization. All students in identified grades were eligible.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Presume no blinding of participants or providers; not feasible due to type of intervention
Blinding of outcome assessment (detection bias)	High risk	No mention
Outcome measures	High risk	Contraceptive use from self‐report
Incomplete outcome data (attrition bias) All outcomes	High risk	Loss to follow‐up: 19 months, 17% (immediately after year 2); 31 months, 21% (12 months after year 2) Exclusions after randomization: 346 students left year 1 and did not enroll in Fall year 2; 95 took baseline survey but were grade 11 or 12
Other bias	Unclear risk	Analysis for cluster randomized trial: multilevel models (levels measurement occasion, student, and school); predictor variables, i.e. baseline responses on outcomes, intervention group, geographic area, and "outcome specific covariates" (related to outcome and intervention; unspecified)