Using the concept of vulnerable populations, we examine how disparities in health may be exacerbated by population-approach interventions. We show, from an etiologic perspective, how life-course epidemiology, the concentration of risk factors, and the concept of fundamental causes of diseases may explain the differential capacity, throughout the risk-exposure distribution, to transform resources provided through population-approach interventions into health. From an intervention perspective, we argue that population-approach interventions may be compromised by inconsistencies between the social and cultural assumptions of public health practitioners and targeted groups. We propose some intervention principles to mitigate the health disparities associated with population-approach interventions.

Studies of`context' are increasingly widespread. These studies often become entrenched in methodological debates rather than being conceptually satisfying. We suggest that part of the problem lies in an inappropriate use of`classic' methods used by epidemiologists to study context and that it may be useful to study, instead, the relationship between agency (the ability for people to deploy a range of causal powers), practices (the activities that make and transform the world we live in) and social structure (the rules and resources in society). We utilise two examples from the current literature to illustrate these problems; the study of lifestyles and social inequalities in disease outcomes. We develop the notion of collective lifestyles as a tentative solution, inspired by Pierre Bourdieu's theory of social action, Anthony Giddens' structuration theory and Amartya Sen's capability theory. Collective lifestyles are defined as an expression of a shared way of relating and acting in a given environment. It is proposed that context is created by relationships between people.

Globally, public health agencies recognise obesity trends among populations as a priority. Explanations for population obesity patterns are linked to obesogenic environments and societal trends which encourage patterns of overeating and little physical activity. However, obesity prevention and nutrition intervention focus predominantly on changing individual level eating behaviours. Disappointingly, behaviour-based nutrition education approaches to changing population eating patterns have met with limited success. Sociological perspectives propose that underlying social relations can help explain collective food and eating patterns, and suggest an analysis of the sociocultural context for understanding population eating patterns. We propose a theoretical framework for the examination of eating patterns as social phenomena. Giddens' structuration theory, in particular his concept of social practices understood as an interplay of 'agency' and 'social structure' (rules and resources), is used to study food choice patterns. We discuss the application of these concepts for understanding routine food choice practices of families, elaborating how rules and resources configure the enabling or constraining conditions under which actors make food choices. The framework assists in characterising how social structural properties are integral to food choice practices, and could direct attention to these when considering nutrition interventions aimed at changing population eating patterns.

time that this paper was being developed and written. Charlotte Loppie reports a grant from the CIHR that funded research reported in a case study in this report. Laurence Moore reports having been a member of the UK MRC Population Health Strategy Group and the MRC/NIHR Methodology Research Programme Panel during the life of this project. He also reports core funding from the MRC and the Scottish Government CSO. David Ogilvie reports a grant from the NIHR Public Health Research programme and a grant from the MRC programme during the life of the project. Mark Petticrew reports a grant from the NIHR to develop a briefing paper. Valéry Ridde reports conducting consultancy work for non-governmental organisations implementing the user fees exemption intervention in West Africa. Daniel Wight reports grants from the UK MRC and the NIHR. Outside the submitted work, he reports core funding from the UK MRC to lead a theme of research on the transferability of interventions.