Hoddinott et al. BMC Public Health 2010, 10:800 http://www.biomedcentral.com/1471-2458/10/800 new and existing group members and the group setting. It is closely related to the ecological, social and beha- vioural theories described above. Group processes and their interactions with the group setting can determine group survival and the intended outcomes, but they have been under-researched in the context of health improvement groups and the relative importance of individual components is unknown. Group Environment Scales (GES) have been developed to systematically mea- sure the norms, values and psychosocial characteristics of social environments [47]. The underlying theory is that environments like people have unique personalities, climates or atmospheres which are important determi- nants of behaviour. GES have three basic dimensions: relationship dimensions which assess the extent to which individuals are involved, for example cohesion, support; personal development dimensions, for example autonomy, goal attainment; system maintenance or sys- tem change dimensions for example order, organisation, clarity, control. GES have been developed in the field of mental health treatment, education and work and little is known about their generalisablity to health improve- ment groups. They have been used to compare self-help groups [23] and these three dimensions seem salient in a wide variety of social settings, although the character- istics of each dimension may vary [34,48]. The dimen- sions we use in Table 3 are adapted from GES to provide a better fit with our data. In particular the per- sonal development dimension seems more relevant to educational or treatment groups and we have reframed this as attributes of the leader and the group partici- pants. As groups are complex systems there is some overlap and interaction between dimensions. We have used the term “group leader” to embrace a range of observed styles which others have defined [9,22]. Variation in the delivery skills of group leaders can theoretically determine the success of the interven- tion and it is important to consider the statistical effects of such clustering in the design [13]. Education, support and behavioural interventions in a group setting are characterised by different communication styles. For example, a group leader may be an advocate of a method, philosophy, activity, seller/deliverer of a “pro- duct” or a facilitator of person centred approaches, for example empowerment, counselling or support [49]. How leaders with personal experience of a condition, for example in commercial weight management groups [21] and the expert patient programme [7], influence group outcomes is largely unknown. Some groups are multifaceted with communication interspersed with activities like relaxation, physical activity, weighing or physiological monitoring. Health service training in group leadership is variable depending on the type of group and the nature of the intervention. For example, Page 7 of 9 exercise groups have standardised qualifications for leaders, whereas in some primary care groups for weight loss, practice nurses are self-taught and learn on the job [21]. The NICE behaviour change guidelines [10] recom- mend that community interventions should: improve self-efficacy; develop and maintain supportive social net- works; promote resilience; build skills; promote partici- pation in voluntary activities; promote involvement in planning and delivery of services and have access to the financial and material resources needed to facilitate behaviour change. Of fundamental importance is having a clearly stated purpose with aims and objectives that are agreed by everyone. However, even with clear aims and objectives, differing interpretations will arise. For example, in a trial of breastfeeding support groups, lea- ders interpreted the word “support” in different ways. Despite a clear protocol stating that support should be woman-centred and based on informed choice, some interpreted “support” as promoting and encouraging exclusive breastfeeding as you might support a football team [16]. Some experts classify groups into either task orientated groups, where individuals or the group have specified goals, or socio-emotional groups where feelings and inter-personal relationships are paramount [9]. However, our group observations suggest that this bin- ary classification may not apply to the complexity of health improvement interventions, which usually com- bine task and socio-emotional objectives [16,21]. A study of cancer support groups illustrates how an analysis of group processes can provide important evi- dence and highlights the difficulties with pre-selecting group composition [50]. Education and discussion groups combining distressed and undistressed cancer patients were compared with a group of distressed patients. The heterogeneous group increased the social comparison opportunities for distressed patients and benefited them. However, undistressed women with breast cancer who had high levels of social support showed a slight deterioration in physical functioning when attending the heterogeneous group, which raised ethical concerns. The authors suggest training undistressed participants to maximise their benefit for distressed participants but to minimise negative conse- quences for themselves. Individuals tend to conform to the attitudes and beha- viours of the majority within a group, and cliques can develop. For example, some breastfeeding groups can be dominated by mothers breastfeeding older infants, which may be off-putting to new mothers joining, but an over-all “feel-good atmosphere” can override personal differences [20]. Studies suggest that conformity and uniformity in groups increases with group size and over time and groups tend to exhibit more extreme attitudes,