Hoddinott et al. BMC Public Health 2010, 10:800 http://www.biomedcentral.com/1471-2458/10/800 differentiates between whether the support is lay or pro- fessional, but not between interventions delivered to individuals or groups [25]. In a systematic review of smoking cessation groups, theories of behaviour change validated for individual delivery, for example stages of change or cognitive behavioural theory, have been assumed to be transferable to delivery in a group setting [1]. This systematic review of smoking cessation inter- ventions [1] is one of few which has specifically analysed outcomes for interventions in group settings and com- pares them with self-help materials, individual counsel- ling, nicotine replacement or no intervention. It concludes that group programmes are more effective than no intervention or self help interventions, but there is insufficient evidence to evaluate whether groups are more effective than individual counselling. Another sys- tematic review comparing group versus individually delivered interventions for weight management in adult obesity found that group interventions report signifi- cantly more weight loss at 1 year follow-up compared with the same intervention individually delivered [2]. A systematic review of group education programmes for adults with type 2 diabetes compared with routine treat- ment, waiting list control or no intervention, found group programmes were effective at lowering glycated haemoglobin, fasting blood glucose, blood pressure, weight and medication use [4]. For cardiac rehabilita- tion, interventions delivered individually at home were as effective as those delivered in a centre to a group [6]. The aims of a group intervention, the underlying behavioural change theories and group processes can determine who attends and both the group and the indi- vidual health outcomes. A one size fits all approach sel- dom meets everyone’s needs and it has been argued that for self care in chronic disease, groups should only be considered for simple standardised messages, where peer support is beneficial or preferred and where a group will save money [24]. Importantly, some groups may increase health inequalities by attracting more edu- cated and higher income participants [17,26,27]. It has been suggested that support groups are more likely to be sought for diseases viewed as stigmatizing, like AIDS, alcoholism, breast and prostate cancer rather than less stigmatizing, yet important, diseases like heart disease [28]. There are inconsistencies in self care group defini- tions, for example in a survey of American self care groups 60% of those identified had professional facilita- tors and the clinical potential for social support in com- bination with professional guidance compared to peer only support is largely unknown [28]. The potential for cost savings with group compared to individual health improvement interventions can appear attractive; however the health economic evidence is mixed and often weak. In a review of individual or Page 3 of 9 group self care interventions, there was insufficient evidence to support the claim that group interventions are cheaper and there are often trade-offs between the numbers of patients treated and the quantity of inter- vention each individual receives [24]. Smoking cessation groups are no more cost effective than intensive indivi- dual counseling [1] and breastfeeding groups provided as part of routine care would have similar costs to indi- vidual health visitor home visits to group participants [17]. Group interventions for weight management in obesity are potentially more resource saving in terms of total health professional-hours involved per participant [2]. Few self care group interventions for arthritis have measured service use and findings are conflicting [29,30]. Why do we need a framework? In the literature discussed above, it is clear that the jury is still out when it comes to deciding whether group or individual interventions are more effective and cost- effective at improving health outcomes. Group processes and interactions have received less attention than dyadic or individual behaviour change mechanisms and little is known about which components of groups contribute to effectiveness. As a result there are many unanswered questions for practitioners and policy makers who aim to establish patient groups to improve health outcomes. The NICE behaviour change guidelines recommend being as specific as possible about the content of the intervention, spelling out what is done, to whom and in what social and economic context [10]. A challenge with groups is to unpick the extent to which outcomes are determined by leadership style, personality, participants’ characteristics or more complex interactions. Having a framework for design and process evaluation is one step towards producing this evidence and we describe this below. The place, setting and context of group interventions The first and crucial stage in designing and evaluating a group intervention is to consider how aspects of the set- ting will impact on all aspects of group processes, com- position and outcomes (Table 1). In a trial which randomised primary care organisations to deliver a pol- icy to provide breastfeeding support groups, the breast- feeding outcomes were explained by the characteristics of the primary care organisation, including health inequalities and deprivation, the amount of organisa- tional change taking place and multi-disciplinary team- work [18]. The breastfeeding outcomes could not be explained by the amount of intervention delivered or the number of people attending the groups. Evaluating how different environmental settings influ- ence behaviour has been relatively neglected in research