Sara L Hayes, Mala K Mann, Fiona M Morgan, Mark J Kelly, Alison L Weightman

In many countries, national, regional and local inter- and intra-agency collaborations have been introduced to improve health outcomes. Evidence is needed on the effectiveness of locally developed partnerships which target changes in health outcomes and behaviours. To evaluate the effects of interagency collaboration between local health and local government agencies on health outcomes in any population or age group. We searched the Cochrane Public Health Group Specialised Register, AMED, ASSIA, CENTRAL, CINAHL, DoPHER, EMBASE, ERIC, HMIC, IBSS, MEDLINE, MEDLINE In-Process, OpenGrey, PsycINFO, Rehabdata, Social Care Online, Social Services Abstracts, Sociological Abstracts, TRoPHI and Web of Science from 1966 through to January 2012. 'Snowballing' methods were used, including expert contact, citation tracking, website searching and reference list follow-up. Randomized controlled trials (RCTs), controlled clinical trials (CCTs), controlled before-and-after studies (CBAs) and interrupted time series (ITS) where the study reported individual health outcomes arising from interagency collaboration between health and local government agencies compared to standard care. Studies were selected independently in duplicate, with no restriction on population subgroup or disease. Two authors independently conducted data extraction and assessed risk of bias for each study. Sixteen studies were identified (28,212 participants). Only two were considered to be at low risk of bias. Eleven studies contributed data to the meta-analyses but a narrative synthesis was undertaken for all 16 studies. Six studies examined mental health initiatives, of which one showed health benefit, four showed modest improvement in one or more of the outcomes measured but no clear overall health gain, and one showed no evidence of health gain. Four studies considered lifestyle improvements, of which one showed some limited short-term improvements, two failed to show health gains for the intervention population, and one showed more unhealthy lifestyle behaviours persisting in the intervention population. Three studies considered chronic disease management and all failed to demonstrate health gains. Three studies considered environmental improvements and adjustments, of which two showed some health improvements and one did not.Meta-analysis of three studies exploring the effect of collaboration on mortality showed no effect (pooled relative risk of 1.04 in favour of control, 95% CI 0.92 to 1.17). Analysis of five studies (with high heterogeneity) looking at the effect of collaboration on mental health resulted in a standardised mean difference of -0.28, a small effect favouring the intervention (95% CI -0.51 to -0.06). From two studies, there was a statistically significant but clinically modest improvement in the global assessment of function symptoms score scale, with a pooled mean difference (on a scale of 1 to 100) of -2.63 favouring the intervention (95% CI -5.16 to -0.10).For physical health (6 studies) and quality of life (4 studies) the results were not statistically significant, the standardised mean differences were -0.01 (95% CI -0.10 to 0.07) and -0.08 (95% CI -0.44 to 0.27), respectively. Collaboration between local health and local government is commonly considered best practice. However, the review did not identify any reliable evidence that interagency collaboration, compared to standard services, necessarily leads to health improvement. A few studies identified component benefits but these were not reflected in overall outcome scores and could have resulted from the use of significant additional resources. Although agencies appear enthusiastic about collaboration, difficulties in the primary studies and incomplete implementation of initiatives have prevented the development of a strong evidence base. If these weaknesses are addressed in future studies (for example by providing greater detail on the implementation of programmes; using more robust designs, integrated process evaluations to show how well the partners of the collaboration worked together, and measurement of health outcomes) it could provide a better understanding of what might work and why. It is possible that local collaborative partnerships delivering environmental Interventions may result in health gain but the evidence base for this is very limited.Evaluations of interagency collaborative arrangements face many challenges. The results demonstrate that collaborative community partnerships can be established to deliver interventions but it is important to agree goals, methods of working, monitoring and evaluation before implementation to protect programme fidelity and increase the potential for effectiveness.