BMC Public Health 2009, 9:207 http://www.biomedcentral.com/1471-2458/9/207 Primary Care Trusts (PCTs) and London strategic bodies, will be delivered in two phases (covering 9 and 11 Bor- oughs respectively) with a 6 months gap between them. The interventions are largely funded by the Big Lottery 'Wellbeing' Fund, while the evaluation is co-funded by the Big Lottery and the Wellcome Trust. This paper describes the process and methods used to evaluate the Well London interventions and their impact on HE, HPA and MH in local communities. This paper was written at the end of the interventions design phase. Interventions delivered by Well London have been drawn from a set of projects suggested by the project partners. The set of possible themed projects included: Healthy Spaces: a project to improve the quality of public space to encourage physical activity and feelings of secu- rity and wellbeing within the local area. Active Living: residents are provided with maps informing them of local resources for making healthy choices; including for example farmer's markets and open spaces. Be Creative Be Well: supports and facilitates local cultural activities to foster social networks and social capital. Buywell: a set of interventions to improve access to healthy food choices in the local shops Changing Minds: local people with experience of mental ill-health are recruited to raise awareness of mental health issues and promote understanding of its impact. DIY Happiness: using humour and creativity and based on theories of positive psychology, activities are intended to reduce the impact of stress and increase psychological resources to cope with adversity. Eatwell: a project to improve diet and nutrition by raising awareness of the importance of diet to physical and men- tal health and making healthy eating easier and more attractive. The exact mix of activities in each area has been decided upon through priorities identified by residents and com- plementarity to the facilities and services already pro- vided. In each site Well London has used an identical process to assess needs, develop intervention components and build community capacity and stakeholder commit- ment to ensure sustainability [16-18]. Each partner organ- isation leads on projects pertinent to their area of expertise. In addition all communities engage in activities intended to strengthen local capacity and community development initiatives. Big Lottery resources allow interventions to the annual value of £100,000 per area. A detailed description of the interventions and their components can be found at http:/ /www.london.gov.uk/welllondon/. To allow for these interventions and the overall approach to be evaluated, the Well London areas were deliberately selected in a manner which would allow a formal Cluster Randomised Controlled Trial (CRCT). This process (described in more detail in the methods section) involved: a) a decision to work at Lower Super Output area (LSOA) level; b) power calculations to ascertain the number of intervention and control LSOAs required to detect clinically important effect sizes; c) selection of 4 of the most deprived neighbourhoods in each of the 20 tar- get Boroughs (measured using the Index of Multiple Dep- rivation (IMD)[19]; d) requesting LAs/PCTs to select 2 from the 4 most deprived areas and e) randomising these to generate one intervention and one control neighbour- hood/LSOA per Borough. Methods/Design Study design and population The study is a cluster randomised controlled trial of an identical community-based approach to needs assessment and design and delivery of complex interventions to pro- mote HPA, HE and MH. There are three components in the evaluation: a) cross-sectional surveys of adults and adolescents using pre and post intervention quantitative measures of HPA, HE and MH; b) a survey of structural and ecological characteristics relevant to health of the intervention areas and c) a complementary qualitative longitudinal study to explore 'how' the interventions affect communities and individuals involved. The imple- mentation of individual projects will also be appraised through a project-specific process evaluation. The overall research design is shown in figure 1. While the approach to the needs assessment, and interven- tion design and delivery, and the types of intervention delivered will be identical in each experimental cluster, the exact content of interventions will be tailored to local needs. Recent literature on evaluation argues that this is valid as "context level adaptation does not mean that the integrity of what is being evaluated across multiple sites is being lost. Integrity defined functionally, rather than com- positionally is the key" [20] Each intervention or control area (cluster) in this CRCT corresponds to a Lower Level Super Output Area (LSOA) a geography created by the UK Office for National Statis- tics (ONS) following the 2001 Census. Each LSOA con- tains between 1000 and 1500 residents, has 800 to 1000 residential addresses and covers about 5–6 streets. Infor- mation covering social, demographic, economic and Page 3 of 11 (page number not for citation purposes)