Background
Intimate partner violence (IPV) against women is a global public health concern. While community-level gender norms and attitudes to IPV are recognised drivers of IPV risk, there is little evidence on how interventions might tackle these drivers to prevent IPV at the community-level. This secondary analysis of data from the SASA! study explores the pathways through which SASA!, a community mobilisation intervention to prevent violence against women, achieved community-wide reductions in physical IPV.

Methods
From 2007 to 2012 a cluster randomised controlled trial (CRT) was conducted in eight communities in Kampala, Uganda. Cross-sectional surveys of a random sample of community members, aged 18–49, were undertaken at baseline (n?=?1583) and 4 years post intervention implementation (n?=?2532). We used cluster-level intention to treat analysis to estimate SASA!’s community-level impact on women’s past year experience of physical IPV and men’s past year perpetration of IPV. The mediating roles of community-, relationship- and individual-level factors in intervention effect on past year physical IPV experience (women)/perpetration (men) were explored using modified Poisson regression models.

Results
SASA! was associated with reductions in women’s past year experience of physical IPV (0.48, 95 % CI 0.16–1.39), as well as men’s perpetration of IPV (0.39, 95 % CI 0.20–0.73). Community-level normative attitudes were the most important mediators of intervention impact on physical IPV risk, with norms around the acceptability of IPV explaining 70 % of the intervention effect on women’s experience of IPV and 95 % of the effect on men’s perpetration. The strongest relationship-level mediators were men’s reduced suspicion of partner infidelity (explaining 22 % of effect on men’s perpetration), and improved communication around sex (explaining 16 % of effect on women’s experience). Reduced acceptability of IPV among men was the most important individual-level mediator (explaining 42 % of effect on men’s perpetration).

Conclusions
These results highlight the important role of community-level norm-change in achieving community-wide reductions in IPV risk. They lend strong support for the more widespread adoption of community-level approaches to preventing violence.