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Table 1 Precision estimates for effect sizes given varied assumptions about control-arm prevalence and between-community variation

From: A community mobilisation intervention to prevent violence against women and reduce HIV/AIDS risk in Kampala, Uganda (the SASA! Study): study protocol for a cluster randomised controlled trial

Outcome Estimated final sample size per site (with 4 intervention and 4 control sites in total) Estimated prevalence of outcome measure Effect estimate Estimate of precision of percentage risk difference (95% CI)*
   Control arm (%) Intervention arm (%) Risk difference (%) k = 0.1 k = 0.2 k = 0.3 k = 0.4
Past year experience of physical IPV (women partnered in past year) 75 (based on 100 respondents per site, 80% having partner in past year and 5% non-response to violence questions) 30.0 22.5 7.5 −2.4, 17.4a −5.2, 20.2 a −8.8, 23.8 a −12.9, 27.9 a
   30.0 15.0 15.0 5.8, 24.2 3.4, 26.6 0.2, 29.8 −3.4, 33.4 a
   20.0 15.0 5.0 −3.2, 13.2 a −4.7, 14.7 a −6.9, 16. 9 a −9.4, 19.4 a
   20.0 10.0 10.0 2.4, 17.6 1.1, 18.9 −0.8, 20.8 a −3.0, 23.0 a
Past year experience of sexual IPV (women partnered in past year) 75 (based on 100 respondents per site, 80% having partner in past year and 5% non-response to violence questions) 15.0 11.0 4.0 −3.1, 11.1 a −4.1, 12.1 a −5.6, 13.6 a −7.3, 15.3 a
   15.0 7.5 7.5 0.9, 14.1 0.0, 15.0 −1.3, 16.3 a −2.8, 17.8 a
   10.0 7.5 2.5 −3.4, 8.4 a −3.9, 8.9 a −4.8, 9.8 a −5.8, 10.8 a
   10.0 5.0 5.0 −0.4, 10.4 a −0.9, 10.9 a −1.7, 11.7 a −2.6, 12.6 a
Concurrent sexual partners (among non-polygamous men partnered in the past year) 75 (based on 100 respondents per site, 80% having partner in past year and 5% non-response to sexual behaviour questions) 50.0 37.5 12.5 0.0, 25.0 −5.7, 30.7 a −12.5, 37.5 a −19.7, 44.7 a
   50.0 25.0 25.0 13.4, 36.6 8.4, 41.6 2.4, 47.6 −3.9, 53.9 a
   40.0 30.0 10.0 −1.3, 21.3 a −5.5, 25.5 a −10.7, 30.7 a −16.3, 36.3 a
   40.0 20.0 20.0 9.5, 30.5 5.9, 34.1 1.3, 38.7 −3.7, 43.7 a
  1. *Based on calculations provided by Hayes and Bennet (1999) [58].
  2. aNo statistically significant difference between intervention and control groups.
  3. IPV, intimate partner violence.