Abstract: We included 98 studies (147 articles). There were 88 core studies: 37 focused on advocates (4 survey-based, 3 instrument development, 30 qualitative focus) and seven on abused women (6 qualitative studies, 1 survey); 44 were experimental intervention studies (some including qualitative evaluations). Ten further studies (3 randomised controlled trials (RCTs), 1 intervention process evaluation, 1 qualitative study, 2 mixed methods studies, 2 surveys of women, and 1 mixed methods study of women and staff) did not fit the original criteria but added useful information, as befitting a realist approach. Two studies are awaiting classification and three are ongoing. Advocacy interventions varied considerably in contact hours, profession delivering and setting. We constructed a conceptual model from six essential principles based on context-mechanism-outcome (CMO) patterns. We have moderate and high confidence in evidence for the importance of considering both women's vulnerabilities and intersectionalities and the trade-offs of abuse-related decisions in the contexts of individual women's lives. Decisions should consider the risks to the woman's safety from the abuse. Whether actions resulting from advocacy increase or decrease abuse depends on contextual factors (e.g. severity and type of abuse), and the outcomes the particular advocacy intervention is designed to address (e.g. increasing successful court orders versus decreasing depression). We have low confidence in evidence regarding the significance of physical dependencies, being pregnant or having children. There were links between setting (high confidence), and potentially also theoretical underpinnings of interventions, type, duration and intensity of advocacy, advocate discipline and outcomes (moderate and low confidence). A good therapeutic alliance was important (high confidence); this alliance might be improved when advocates are matched with abused women on ethnicity or abuse experience, exercise cultural humility, and remove structural barriers to resource access by marginalised women. We identified significant challenges for advocates in inter-organisational working, vicarious traumatisation, and lack of clarity on how much support to give a woman (moderate and high confidence). To work effectively, advocates need ongoing training, role clarity, access to resources, and peer and institutional support. Our provisional model highlights the complex way that factors combine and interact for effective advocacy. We confirmed the core ingredients of advocacy according to both women and advocates, supported by studies and theoretical considerations: education and information on abuse; rights and resources; active referral and liaising with other services; risk assessment and safety planning. We were unable to confirm the impact of complexity of the intervention (low confidence). Our low confidence in the evidence was driven mostly by a lack of relevant studies, rather than poor-quality studies, despite the size of the review. Results confirm the core ingredients of advocacy and suggest its use rests on sound theoretical underpinnings. We determined the elements of a good therapeutic alliance and how it might be improved, with a need for particular considerations of the factors affecting marginalised women. Women's goals from advocacy should be considered in the contexts of their personal lives. Women's safety was not necessarily at greatest risk from staying with the abuser. Potentially, if undertaken for long enough, advocacy should benefit an abused woman in terms of at least one outcome providing the goals are matched to each woman's needs. Some outcomes may take months to be determined. Where abuse is severe, some interventions may increase abuse. Advocates have a challenging role and must be supported emotionally, through provision of resources and through professional training, by organisations and peers. Future research should consider the different principles identified in this review, and study outcomes should be considered in relation to the mechanisms and contexts elucidated. More longitudinal evidence is needed. Single-subject research designs may help determine exactly when effect no longer increases, to determine the duration of longitudinal work, which will likely differ for vulnerable and marginalised women. Further work is needed to ascertain how to tailor advocacy interventions to cultural variations and rural and resource-poor settings. The methods used in the included studies may, in some cases, limit the applicability and completeness of the data reported. Economic analyses are required to ascertain if resources devoted to advocacy interventions are cost-effective in healthcare and community settings.

Plain-language summary: We found 98 studies from 15 countries. Of the 88 core studies, 37 asked advocates about their views and experiences and seven asked abused women about advocacy (two of these also asked staff). The other 44 core studies helped us understand the way advocacy works and how effective it is. We included 10 additional studies that did not fit the original criteria but added useful information, as befitting a realist approach. Of these, three were randomised controlled trials (RCTs; a type of experiment in which participants are randomly allocated to two or more interventions), one was an intervention process evaluation, one was a qualitative (e.g. focus groups, interviews) study, two studies used mixed methods (a combination of qualitative and quantitative research) to explore women's experiences, two were surveys of women, and one was a mixed methods study of women and staff. We were unable to obtain the full texts of two studies that we thought might be core and three further relevant studies are still ongoing. Advocacy interventions varied considerably in duration, participating staff (e.g. nurses, psychologists, social workers), and setting (e.g. healthcare settings, domestic violence refuges or shelters). In the studies, women and advocates agreed that the following were all important parts of advocacy: education and information on abuse and on women's rights and sources of help (resources); active referral to, and help in accessing other services; assessment of risk of repeat abuse; and safety planning to avoid it. Trust in the advocate is important and more likely when the advocate and the woman share an ethnic background or the advocate was also abused. Advocates must help women consider their best options, depending on things like ethnicity, immigration status, where they live, the severity and type of the abuse experienced and finances. There are trade-offs when making decisions to reduce the abuse and women's safety was not necessarily at greatest risk from staying with the abuser. Advocacy could potentially have some benefits for abused women, if undertaken for long enough, but its goals need to match each woman's needs. It may take months to have an effect. Two studies (one involving the police and one in an antenatal clinic) found that where abuse is severe to start with, some interventions may possibly prompt the abuser to increase the abuse. Advocates want to help women and can get stressed if they do not feel helpful enough, so they need support from organisations and other advocates, including repeat training, debriefs, and funding to do their job well. Our confidence in the key findings varied between moderate and high. However, some themes (the effect on outcomes of women being physically dependent on their abuser, being pregnant or having children) were less well supported by evidence and further, good-quality research is needed to confirm findings. Researchers should be careful when choosing how to measure abuse so that measures have more meaning for advocates and abused women, thus increasing the usefulness of future reviews. Further evidence from studies where participants are followed up for years would be helpful. More economic analyses are needed to establish if current advocacy interventions are the best way of spending money for abused women.